Resin kit mfgs find their nitch producing kits for those who want something- a less popular subject- that would not otherwise make money in a die-cast styrene kit. Resin kits take much less investment up front. However, since these cottage industries do not sell nearly as many kits, they cannot afford to advertise very much. Also, bigger wholesalers and major hobby chains stay away from their products. Thus, it is much harder to be aware of these kits. FSM forums are one way to find them. Ask about a desired subject in the appropriate genre forum (in the modeling subject domain) and hope someone there will know of one. Also, belonging to a local model club gives you friends to ask.
The resin kits, because they are produced in lower quantity, tend to be expensive, not of major mfgr quality, and sometimes require modeler to supply some materials and aftermarket parts.