homewound TC power supply transformers?

I have a small 150 watt NST.  Does anybody know if it is possible to
rewind the transformer for more watts(with fatter wire), or will my core
saturate and effectively limit the power?  Does anybody know a source for
transformer cores so I can wind it myself to save money?
Thanks in advance
Get the Internet just the way you want it.
Free software, free e-mail, and free Internet access for a month!
Try Juno Web: http://dl.www.juno-dot-com/dynoget/tagj.