I had no idea that the '94 Supra had 4" speakers in the doors... I always thoght that they would be larger...
Not having taken apart a Mk4 door, I have no idea what your mounting depth is like, but I know that on my '89, the mounting depth was very shallow. You can use a spacing ring to get a bit more depth from it, if need be.
Personally, I've never heard a 4" speaker that I found satisfying, but YMMV.
If you don't want to get into a bunch of custom work, then your best choice is likely going to be to get a set of 4" speakers, and make 'em fit.
Redrilling holes usually means that the speaker holes in the factory speaker are not at standard radius, and/or spacing around the speaker. You need to drill in new screw holes. Usually not a big deal.
FWIW, new factory speakers are likely to cost more than decent aftermarkt ones will.