Does any one make a 1" clutch 10 driver #35 chain

If your buddy has already gone to the biggest rear axle sprocket size he can get away with, and still needs to go to the smaller clutch sprocket, then there are two things that can be done:

Have the crank end machined down to 3/4" to accept 3/4" clutches. (Or maybe get a new crank.)
Use a jackshaft to drop the ratio and put a 3/4" clutch on the jackshaft. (2-cycles do it all the time.)

This sounds like an awfully small track!