There are many websites that have good circuit diagrams to start with. Old Treble boosters and fuzz faces are easy to start with. Casings can probably look them around at TY music. But yeah, the web has it all to start with?
They may come shipped together with instructions, and if you are not game to do it yourself. You can try a Famous sim lim tower basement uncle who does it at his shop, or at Can Audio music shop at 02-22.