One of the things I do to fill employment gaps is to "space-sit" at a theatre that I sometimes stage manage for. When one of their spaces isn't being used, they will rent it out to other theatre companies or groups, and they need to have a staff person on duty so unlock doors, answer questions, sometimes turn on equipment. It's not hard work, and I already know my way around the building, so it works out pretty well.
I've also done work for a dance studio, a documentary film festival, a non-profit arts organization, and other things- almost all of which I've found through friends, colleagues, or relationships I've developed with arts organizations over the last few years. I just make sure that the people I know are aware that I am looking for work and am open to opportunities when they come up- it's surprising how well it works out. Being open to doing other types of work helps a lot- and broadens my experience. I don't do much (if any) work that isn't arts-related in some way, and almost all of it is somehow theatre-related, even if not production work.
Maybe you could see if any of the theatres you work at have non stage management opportunities available over the summer.