I've never done it. That said, I have an in-law (outlaw???) who really isn't that good a pianist, to be honest, who has, successfully. Many areas have a variety of amateur or semi-amateur orchestras who might be quite happy to have a decent pianist (as I suspect you are, from your posts!) play with them from time to time. How would I go about it were I to give it a shot? If I knew someone in the organisation, I might ask them for an introduction to the conductor. If not, being older and quite accustomed by now to having folks say some variation of "no", I'd probably try to arrange a meeting with the conductor... can't hurt.
Good luck!