The only ready-made adjustable ones I’m aware of are Premier. According to the website, they’re a tenner a pair. I know Billy offers trade packs but I don’t know the price.
LG miniatures do a set of castings which don’t adjust but perhaps could be made to, they’re £18.
I expect Ragstone do something similar.
I‘m sure most if not all the kit suppliers would sell the castings
i guess it’s a question of what breaks the bank, or DIY which I fear looks like hard work.
if you do go with Premier ones, nip the end of the screw to prevent the trunnion coming off. You can imagine how I know.
best
Simon