We can supply most makes and sizes of ring to fit modern and older, 'obsolete' chainsets. The over-riding parameter for chainrings is the P.C.D. (Pitch Circle Diameter). This is the diameter of the (usually 5) fixing bolts. Unfortunately this is difficult to measure accurately but perhaps the following article can help...
For 5 arm rings you can just multiple the distance between 2 adjacent bolts by 1.7 to give the BCD.
See our info page here
If in doubt ask us and we will do our best to help.