I just did a quick survey of all my cameras that have no film loaded in them.
Smooth pressure plates:
- FED 2
- FED 5
- Kristall
- Kiev 15
- Canonet QL 17
Dimpled pressure plates:
- Zenit 122K
- Zenit AM
- Zenit APk
- Zenit KM
- Vivitar V3800N
- Chinon CE-4s
- Fujica ST-801
I've also got some cameras with film loaded that I couldn't check, including a couple more K-mount cameras (a Ricoh XR-X 3PF and a Pentax P30t). I'm not positive, but I think they both have dimpled pressure plates.
If you don't want to spend a fortune, a FED or Canonet would be a good choice. (FEDs often have lenses with small-diameter filter threads, which could conceivably lower the cost of filters for use with infrared film -- but check on the details to be sure.) FEDs either use meters that are located outside of the filter path or use separate handheld meters; the Canonet's meter is located above the lens but within the lens filter diameter, so the meter is affected by the filter.
If you really want an SLR for this purpose, I might start looking at older Zenits. (The Kristall is essentially an early Zenit by another name and with art deco styling.) Something like a Zenit E might have a Kristall-style pressure plate. I don't know when KMZ (the factory that made my Kristall and all my Zenits) switched from the flat to the dimpled pressure plate; it could have been any time from 1962 to 1993, based on my cameras' serial numbers. Of course, there may well be Japanese SLRs with flat pressure plates, too. The fact that the Canonet has one suggests that checking early Canon SLRs might be worthwhile.
Here's another thought: Perhaps it'd be possible to transfer a flat pressure plate from a camera that has one to a camera with a dimpled pressure plate. I wouldn't want to risk this with a camera that's important to me, but you might try it with a couple of semi-disposable cameras bought off of eBay. At best, you'd have to unscrew and transfer the back plate. At worst, you might need to secure it in some jury-rigged way, such as with epoxy.