Mouser more then likely has various sized enclosures of a wide variety of sizes from small ipod/rc-esc size to very large wall mount enclosures. The products tend to be more expensive because they are certified in some manner, the smaller enclosures dont seem to be more then $5-15. I have a local regional electronics/electrical commercial supplier store of similar category to Mouser but smaller that from my cursory glance sells countless products from Hammond, Mid Atlantic. Lots of materials to choose from, ABS, Metal, Plastic. You could also look at Ardruino products which might have cases for their projects.
Or just find random cheap generic enclosures on ebay/amazon/ali's.
Reminds me of Dollarama tote boxes, you look at them wrong and the plastic cracks.
What size do you require?