Try 4atvtires.com (ATV Direct) has MudLite bigfoot kit for $370.00 or pvpowersports.com or you may just need to do a web search and make some calls. I bought stock size tires for about $210 for all four tires and that included shipping. I just can't remember the site I bought them on. atvpartsworld.com is another good site. If you are doing some extreme mudding I would not only look at a real mud tire (mudzilla or 589's), but also go as big as you can. I tried some real deep mud a few weeks ago and the 25" Mudlites were just too short to handle it. 28" tires would have done much better. Since I usually don't do that much extreme mudding, though, it didn't make sense to spend the dough for the big ones.
I have considered cutting off the bottom of the front fenders too since they seem to get hung up. They hang about 2 in. lower than the footwells and when I got in the thick stuff they seemed to get hung up when backing up. Has anyone else thought of this??