The hard drive in your laptop is almost certainly an IDE (aka PATA) drive.
Mainstream SSD drives are only available as SATA drives and so are NOT compatible with your PC (different physical interface / connections). That's aside from a number of other issues that you could encounter.
If you are prepared to try a IDE SSD (which will likely be some sort of relatively obscure brand), just google for IDE SSD (you'll find some on ebay). In principle they should work, but being obscure brands I would be a bit wary.
If you just want a larger 2.5inch IDE traditional hard drive, that's fine (although they are probably becoming thin on the ground - ebay probably the best bet).