Look into INTEGRITY from Marvin they use a fiberglass material called ULTREX and it comes with a wood grain material or Wood to the interior.

Wood grain apparent on a finished wood window is a sign of poor materials or workmanship. Why would you want to emulate that?

Mightanvil, thats an odd response, given that staining wood is the commonest form of coloring wood

I definitely like the Integrity product

akachrisinmass
The OP asked about wood grain "texture" on the outside of a fiberglass window which I believe would look like paint had been applied over a poorly prepared wood window... something I would not want to emulate. Are you saying that stain on textured (raised grain) wood is the most common form of exterior window finish?

m.lloyd
The exterior of a Marvin Integrity fiberglass window is painted with a perfectly smooth Kynar paint finish in pebble gray or stone white. The interior is real "satin smooth furniture grade" pine left natural or factory finished in white. To my knowledge Integrity does not offer any other "wood grain material" and I just went over an Infinity order with a Marvin dealer this morning and he covered all the options. Marvin makes an all-fiberglass "replacement" window called "Infinity" with a synthetic interior simulated wood finish called "Everwood".

Regarding a "textured" exterior window finish:
It's possible that Andersen offers an exterior textured finish on its "Fibrex" (wood fiber and PVC) clad "Renewal" replacement windows but that's just a guess because I either saw a Renewal or an early Woodwright with a texture years ago. I thought it looked really bad and I haven't seen anything like it since.

Infinity double-hung
This is a good window but it has some limitations. It is offered in a limited number of sizes and no custom sizes; it offers a permanent exterior and interior muntin but only in the same pattern as the snap-in grilles, no variations with no internal spacer.
The sill has no overhang or drip (well, a tiny useless one) so it needs an additional sub-sill to keep it from leaking when the sealant at the top of the exterior finish fails.
The nail-fins are thin and slide in at installation time so they are not water tight and they don't overlap at the corners. The sticky corner seals provided are pretty silly. Careful attention to flashing in the field is needed with this window but probably no more than most nail-fin windows.
The exterior projection of the jambs is only an inch which works out well for 5/4 (1" thick) casing trim but the sill is thin (1/2"). It looks very good with a sub-sill.
It limits what a designer can accomplish but it is a better window than most in its price range.

I was interested in a window whose exterior looked like real wood, i.e. mahogany stain on wood grain fiberglass, without the upkeep. Similar to the doors available now.

Simulated natural wood fiberglass doors are made with a compression-molded fiberglass skin on a wood frame filled with foam insulation. The frames of high quality fiberglass windows is are made with rigid pultruded (opposite of extruded) fiberglass structural elements which are painted in the factory.

I doubt these technologies will come together anytime soon.

The leaders in fiberglass doors and windows are:
Milgard, Therma-tru, Marvin, Pella, PlastPro, Duxton, Jeld-Wen, Comfort Line, Graham Architectural Products and Fibertec.

I still don't understand why anyone would want a simulated furniture grade hardwood to be textured.

I think they simply want to stain fiberglass windows to match their stained fiberglass door.
Let's face it. Most "historic" looking buildings want to look like the old craftsman windows, but our society is too lazy to maintain wood windows. So we develop cladding and composite units to lower maintenance requirements. The irony is, that now people want the low maintenace to look like the wood that we didn't want to maintain in the first place.
Because fiberglass windows are made very differently from fiberglass doors, the stainability is not possible at this time.

What's wrong with a nice white window that doesn't need painting?

I personally like the look of wood..especially in a more hi end home BUT living now in the PNW...and my Marvin wood clad windows are rotting I might be rethinking that!

I would maintain wood BUT the wood now days will not come close to the longevity of wood harvested prior to say 1950? So why bother? yes and besides rotting the Marvin casements are also going to need refinishing..seem pointless since they are rotting(16 years old) But really no surprise cuz most stuff made now is junk and has limited life expectancy! A cunundrum to say the least!