you can get parts on eBay, often from CA sellers.
just post what you need someone will help you find it.

if the rear brake ceased up it's likely caused from rusted/corroded brake poison chamber.
take it off, disassemble, clean with a solvent, dry, then grease it up and resemble..

don't freak out about these things nor rush to fix and just end up breaking something worse.
as cheap as this bike is, it's equally as simple.
and except for push rods, there are plenty of replacement parts to be had.
just not every single part like a rear brake piston for example. if you actually needed one, you won't likely find one, but rather need to get an entire caliper... but it's available