Putting suspension on my friends BMX bike worked out okay, he had an old tony hawk BMX(we call it the tony cawk) and he put the suspension from an old walmart bike on it, he said he had to remove a few washers or seomthing to do so but in the end it actually worked. if you are going to put suspension on a BMX you probably wont find some specifically for BMX, your best hope would be to find a walmart bike with suspension forks that fit your bike. Btw at this point tony cawk is a 3 wheeled Bmx bike with shocks in my garage, just thought i would share that.
Please be kind I am only a beginner :]