Welcome to the world of bike restoration.
Improvisation is the name of the game.
Your CL-175 will probably work fine with a replacement head gasket made from oil proof gasket material.
Trace the old gasket carefully or transfer the shape with a fine coat of wet paint.
Make sure you don't miss any oil holes.
Clean any fuzz around cut holes in the new gasket so it wont end up in your oil.
On a higher compression engine a gasket made from soft copper or aluminum is often the ticket.