From the "Hardware Random Number Generator" article in wikipedia:

The Commodore 64 provided a hardware random number generator based on its soundchip, the MOS Technology SID 6581. Random bytes can be fetched from memory address $D41B as long as the third oscillator's waveform is set to produce random noise.

But this will be hardware specific and there is no seed.

You can always code one for yourself.

There are very simple pseudo-random generators depending on speed and quality you want.
The linear congruential is the simplest that I know of, althought the middle-square is very easy to understand.

I think I remember that the c64 used the linear congruential method

I do not know which is the fairer method, but they are pretty good for games; not for simulations or encryption.
There is a lot of info out on the net, wikipedia is a very good start, although their categories are a mess.

Start with Random Number Generator and then Pseudo-Random Number Generator.