All classic MacOS files can be found via this link:
http://lowendmac.com/2013/classic-mac-os-downloads-and-updates/Apple itself hosts up to OS8.x and it is available to download for free, but they tend to rearrange files so it can be a bit of a hunt.
In regards to performance, try experimenting with different drivers. It can make a huge difference.
Disregard comments suggesting it's not worth it. As many users and videos show it can be very similar to an equivalent specced Mac (the myth that it's faster is inaccurate, but the difference is in the realm of %25).
