When it comes to hard goods, the first thing to mention is that anything that is to be sublimated must have a polyester coating. There are a number of distributors, among them, who sell sublimatible blanks,so finding a source for hard goods to sublimate shouldn’t be too difficult. The problem here may be that a decorator would be spoiled for choice, faced with such an array of blanks from which to choose. It should also be noted that mastering the technique necessary for sublimating some hard goods may take time and practice.
Sublimating hard goods by transfer paper may also require special jigs or platens for a heat press, so that should be considered as well.
In the final analysis, the items you sublimate will most likely be determined partly by what the market wants, partly by what you enjoy doing, and partly by what items you put in the effort to sell. There is no hard and fast rule about what sublimated good will work for every situation. It’s up to you to do the research and to know your market well enough to make educated choices about what sublimated goods to stock.