For coils, rather than buying new ones I'd send mine to "Coil Man" Ron Patterson or "Coil Doctor" Brent Mize (you can Google them). Ron rebuilt a couple of sets for me, and his work is top notch.
New reproduction parts range from excellent to miserable. Parts dealers I've bought from with good results include Lang's, Chaffin's, Bob's, Snyder's, Bird Haven, Fun Projects, and R.V. Anderson. A lot of people avoid Mac's because of their reputation for less-than-wonderful service. Earlier this year the boss at Mac's acknowledged their problems and said they were going to do better, so maybe they're OK now. I will say that Mac's catalogue, with its excellent illustrations, is a handy reference work. Some of the dealers I listed produce parts that are sold by the others. One example is seat springs. The ones you buy from all the dealers are made by Snyder's.
If you wonder about the quality of a particular repo part, ask about it on the MTFCA forum. It's a very active bunch of T guys, and you're likely to get input from several of them.
There are a lot of sources for used parts, including dealers, auctions and swap meets. Being in Texas, if you're bitten by the T bug you'll want to go to the prewar swap meet in Chickasha OK in March. Nothing after 1942 is allowed, and it's wonderful. Even if you don't buy anything, it's a good trip.