The T-70 takes the same diopters (S-series) that will fit the FTb, FT, Pellix, etc. I assume a viewfinder cover from a F-series camera will also fit on a T-70.
If no cover is at hand, use black tape or make a cover from some plastic sheet and U-profiles, or even more simple: put a plastic sheet in a approriate cup.
I got a lot of FD cameras, but only one hard eyepiece cover...
Some Canon rubber paddings for their camera-straps have a rubber eyepiece-cover inserted.
The T-70 takes the same diopters (S-series) that will fit the FTb, FT, Pellix, etc. I assume a viewfinder cover from a F-series camera will also fit on a T-70.
All A-series Canons have the same viewfinder size as the FTb, etc. So any of them should fit the T-70. But viewfinder accessories for Canons F-series (F-1, F-1n, New F-1) are round, so they will not work.