Hey guy, welcome to the forums. The vast majority of the working parts on these machines can be obtained from a local NAPA autoparts store. In fact, if you call Terramite they can often give you the NAPA part number. On the Terramite website you can find a downloadable owners manual and parts manual. Its worth printing out and keeping handy. As I recall, I think Terramite lists different outrigger pads in that manual, so they would be available from Terramite.
There are few companies making "accessories" or aftermarket parts for these machines. I was able to have a Piranha tooth bar made byBxpanded, a site sponsor, that has been a great addition and I highly recomend. I have added a Terramite ripper tooth for the backhow which works well for stump removal, but is a little short for any real trenching. I have also changed out my smooth front tires with a pair of UTV tires to provide a little more steering control in slick conditions.
I hope this helps. Let me know if you have any other specific questions. Where are you in Pittsburgh?
Terra Joe