Can anybody tell me where I can get a 4>1 collector to take 4x1 3/4" to 1x2.5".

Have you tried MNR

Good Fab

These may be able to help.

Just depends how much you want to spend...............

not too difficult to do it yourself. The fancy blended collectors do not give a great advantage unless set up on a rolling road. Just dumping 4 primary pipes into a cone shaped collector seems to work fine. See DaveVizard on the net for description