An inexpensive way to get intricate solder preform prototypes is to cut them from solder ribbon or foil.
I just got off the phone with a number of material suppliers and I feel like I have hit a wall. I want to order a few custom machined metal blocks to fit into a piece of my test equipment but the quotes I am getting back are far more expensive than I am willing to pay since these are one-time use samples. To make this evaluation possible, I am going to order standard solid blocks of metal. I will ask my machine shop to form the blocks into the special shape that my project requires.
This technique is a larger scale of what I encourage others to do when they are in the process of evaluating preforms. Simple geometries are not typically a problem, however the set-up for an intricate preform design can be quite expensive. If you are unsure whether the preform will work in production, it is a good idea to test some prototypes. An easy way to do this is to order a solder ribbon and cut the sample preforms from it. This will speed up the time it takes to get the samples, and will typically be less expensive.
The application note on practical suggestions for solder preform design has some other tips for inexpensive solder preform prototypes.