There are a number of hunter/jumper barns in the area. There is also the Maine Hunter/Jumper Association which holds shows. I am located in Berwick, ME, which is on the NH border and south of Portland. I run a lesson and sales barn, and have horses that do everything from beginners to advanced riders, and have horses capable of the 3’ and 3’ 6" levels. I allow students to show my school horses as well. Currently I have too many school horses, and really need to downsize–I have 21 available right now, ranging from small ponies to large warmbloods and drafts/crosse.
In addition, in the Portland, ME area there is Kane Kountry Farm (at this point I do not recommend her–she is a good instructor, but as she has gotten older she has gotten very difficult to deal with, but if you can deal with her, she is fine), Kerry Haars, Royalsborough Farm in Durham, Me (just North of Portsmouth), Avalon Meadows in Hiram, ME (that may be closer to you–she seems like she would be a decent instructor, although I have never seen her teach. I think she has a nice place), Avalon Meadows in Otisfield, ME. There used to be a lot more in the Portland, ME area but they have closed/moved. I think Ginger Klingenstein-Albert may still be in the area (Venture Farm) but I am not sure. Also, at Pineland Farms I heard there was a new hunter/jumper group that is in there renting stall. (Pineland is in Gray or Cumberland–not sure which–which is near Portland, ME)
It can be hard to find the hunter/jumper barns in the area. There is also in NH in Wakefield Annie Hutchinson–I don’t remember what she is calling her farm, but she is a hunter/jumper person. There are also a number of barns down near me.