New Bridge?

So, I've been given a Thunder 1 bass that was sitting in a building for at least four years. The finish is coming off the bridge, the screws are rusted, and I can't adjust the G string at all. Where would I be able to find a new bridge that would fit my bass?

Better still,  restore the originals! 
Soak them in thinners overnight then remove the screws/saddles.  Polish the brass and reassemble,  easy, cheap and satisfying

You could always re-finish the one that's on it? If you're dead set on replacing it, I'm sure someone will have more idea than me as I only have a Spectrum bass.
I think you need one with a similar string spacing to the original....

I would definitely love to keep the originals. I just didn't know if it was possible or not. I'm going to try to keep it, but I don't know if I can salvage it with all the rust and everything. I can't get one of the screws to turn so I can adjust the G string at all, that's the part that I'm most worried about. But I'll see if I can get it to work!

Again, soak it in paraffin /petrol/thinners overnight at least, then maybe heat the screw with a soldering iron to shift it. 
Is this brass or chrome hardware?

Okay I will definitely try that.
It's brass.

Brass is easy to restore, either soak it in solvent overnight to remove the old sealer, or use paint stripper if you have to, then polish it up and re seal it, just like new.

Okay, I will!
Will this work for the volume and tone knob as well? Both are brass and the finish is peeling off them as well.

Yep, works fine, though getting the corrosion out of the knurled sides is time consuming, I've started using a medium wire brush attachment on the dremel, makes short work of it.

Okay, thanks for the tip.
By the way, I know this isn't related to anything else, but can I use any kind of stain or paint on the bass or does it have to be a specific kind? (Like oil-based, for example.)

Anything goes

Great, thanks!

Am plus oneing the wire brush for the knurled knob edges. Is plus oneing s thing?

I'm not sure exactly what you mean...?

Also, one last question, the tuners are chrome/steel and have some rust on them as well. Would soaking them in the thinner work too?

Would soaking them in the thinner work too?

Definitely not!
Mix some bi carb(baking soda) powder into a paste.

You can take the tuner buttons off and soak them,  the tuners have plastic crush washers in,  can't soak them in a spirit. 
Soaking chrome wouldn't do anything anyway,  do as westbone sais above.

Also lubricant deep down inside there.

Good point

If they're chrome or nickel, Autosol metal polish works pretty well if you are patient.

Okay, thanks! I feel like I have a lot of questions... Thanks for being patient and answering them all!

Okay, I've got another question for you guys. I was going to sand down the neck of my bass because the color that I painted the bass and the finish on the neck really clash now. Is there anything special I need to do while sanding down the neck? I guess I was just concerned that I might do something to bend the neck or something like that.

Not really,  just go carefully and don't apply unnecessary pressure. 
Ive even started using the palm sander on necks now, just letting it do the work.