New to this board but have owned a 1992 Camaro RS since 1992

The car only has 19,000 miles on it but last week the speedometer and odometer quit working I have been told the first thing to look at is the speed sensor in the transmission it is a T55 speed the problem is I cannot find the proper speed sensor which is a smaller diameter than the ones I see for sale

I really have two questions one does anybody know where I can get the proper speed sensor the second what other areas can I check to see why the speedometer and odometer do not work

Any help would be grateful thanks