a common trick is to replace the window, but paint it black inside

Not a "trick" but a way to retain the original look when you can't match the old bricks.

Sometimes I can't even find ten-year old bricks. Keep an eye out for local demolitions.

You could replace the window after painting a trompe l'oeil of curtains, etc. on the inside of the glass.

If you still have the frame in place, buy wood shutters and fit them in the window in the "closed" position. This is more convincing if the rest of the house has shutters. It's a traditional way to hide "blind" windows in facades. A blind window is sometimes called for to maintain symmetry, but an actual window opening is impossible due to issues on the interior.
Casey

no_clever_name:

You could have enough matching brick carefully removed and cleaned from a more inconspicuous area, say behind a bush near the foundation, and have the replacements installed there.

You'll have to pay for a mortar analysis also. You don't want to go through all this trouble and expense and then not have that match either.

Expensive, but your problem will disappear in a few years of weathering.

Thank you all for your responses! (Had a very busy week and could not check for responses until now.) I really appreciate the variety of responses, but I'm afraid most of them won't work for one reason or another. (I will say I was particularly intrigued with the idea of moving brick from a less visible area of the house, but I think that is likely to cost more than I'm prepared to spend.)

Since I posted, I've spoken with a local architect who has lived and worked in this area for a long time, and I think we have a solution that should be reasonably attractive and not outrageously expensive. There is a large wood or stucco (you'd think I'd know that after living here so long...!) "bay" area on the outside of the dining room, on the same wall as "the window that was." The thought is to take off on that idea, probably re-frame the window area in some fashion, and fill in the window with a material similar to the bay. Then 2-3 decorative medallions would be placed in that area. This was actually my original idea, inspired by a decorative plaster frieze over the front door, but I couldn't find a medallion or other decorative element that was proportioned properly for the space; however, the architect was able to find a source with a couple designs that will fit the character of the house.

Thank you again for taking the time to share your creativity with me!

I hope you will post a pic of the finished project. I'd love to see it.
Kathy