Someone want to give me the low down so I can be lazy and not have to do the research myself? I would really appreciate it.
The short answer is that there is no short route to what you seek.
If you really want to cast, your best bet is to read the last four or five years of this forum.
Casting parts went from an obscure practice by just the elite puzzle builders to flowering into a real craft by a good portion of the community. Multiple new techniques were developed and refined that made the older methods look painful.
I don't think anyone who has had any success in casting parts will tell you it is either easy or cheap to get started. I was pretty lucky in that I didn't start until some of the better methods had been developed, and I took the time to read a lot which let me avoid a lot of mistakes. I knew what to buy and generally what to do. With some patience (and perhaps a bit of obsessiveness), I was able to get good results
on my first try, but I had plenty of mistakes later.
The patience you put into it is a large determiner of the quality of the result. So if you don't have the patience to do research, don't expect to get a good result.
I would suggest posting on Marketplace. There is a chance someone has a broken Teraminx and might be able to help you with a part (one broken teraminx could supply a lot of spare parts to the whole community...). Another option is to contact one of the sellers (like excalvin, for example) and see if they might have a spare to sell you.