Does anybody make resin replacement triangular handles for US armor engine access doors...need some for a 1/35 AFV club M41

No idea but why not make your own? Get a length of triangular styrene or other stock of the right size, coil wire round it and cut along one face to make yourself a load of them. If you can’t find any triangular stock small enough, try heat stretching some that is larger.

There are some in various old Eduard sets including the one for the old Tamiya M41.

But they are flat . You'd be better off doing your own since the real deal are round. A piece of wire corded around a triangular needle file works well.