Can't reccomend anyone in your area but I've had a few frames done local to me with varying standards of finish and the quality has not always reflected the price I've paid. You won't get a show standard finish with powder coat but you should be able to get something pretty good and it is tough as hell. Stove enamel is no where near tough enough for a trials bike IMO.
My top tips would be
Make sure they know you are looking for a decent finish. I've had frames back with pitting and grit in the surface and they've just told me. "It's an industrial finish, that's what you get" It shouldn't be!
Try and find a place that's done a few bike frames/forks so they have an idea of what they should and shouldn't be masking. Always best to run through with them what you want masked of anyway.
See if you can pick up a couple of old style steel bottom bracket cups from your local bike shop. Doesn't matter if they've been used as long as the threads are good and the right type and size. Most frames are 26TPI (i think). Put these in to protect the threads and you can take them out when you get it back (you may have to cut the powder coat with a stanley knife to get them loose. Your local bike shop should be able to confirm the thread type and might even be able to reccomend a good powder coaters.
Last thing, the colours on the charts they show you might not be exactly the same as the finished product so be prepared for a slight variation in colour.
Think that's about it.
Good luck Oh yeah, make sure shot/grit/sand blasting whatever is included.