DIY with individual boards set at the same angle as the original, but nailed onto a frame you can set into the area under the porch.

Have the contractor leave a "lip" for the lattice to be nailed onto.

Back it with black window screening to keep varmints out, and make sure you treat the wood with a waterproofing compound and have it above the ground level.

If rodents are a problem, back the lattice with hardware cloth to keep them from digging under it (look up how to vermin-proof a chicken run for details)

Woodway Products lattice is carried by many lumberyards.

Here is a link that might be useful: Woodway Products

Exactly as Renovator has linked, very good products and available from most true lumberyards.

The only way to get authentic old-style lattice is to make it yourself. We have made lattice panels for several jobs, out of western cedar and Spanish cedar. A simple alignment jig of spacers stapled to a sheet of plywood is all it takes to assemble them very rapidly.
We used 1 1/2'x1/2" thick laths. A 1/4" crown staple gun puts them together very sturdily. And nothing you can buy beats the look of heavy old lattice.
Casey

as i stood in my utility room picking paint out of 100 year old window hardware with a thin metal pick, i realized that "painstaking" is pretty much unavoidable if you want things to be right.

Woodway...looks nice, but yet another company with no local distributors in Columbus Ohio...I'm sure shipping would be outrageous so I guess I'm stuck with big box or building my own. :( Same deal with half-round gutters.

Sarah - I can't help much with the lattice, but can tell you that the half round gutters are readily available from a couple of sources. One is in Erie, Pa and the other is in Kalamazoo, MI. I'm sure there are other sources also, but we were very successful in getting exactly what we wanted from Erie.

Good Luck