For the last 20 years I have used a normal contact adhesive as a thread lock on silencers etc. I just dip the bolt in Dunlop Thixofix - a rubbery type of DIY contact glue which seems to have a Petrol (gasoline ) solvent base and is a buttery non stringy goo. I previously used Evostick - solvent type- just a bit runny/stringy but otherwise the same. I think any rubbery type will do.
The bolt release easily when you want them to but never come loose on their own. Even old engines come apart years later with no problems and the threads can be cleaned with solvent if it wont peel off.
Obviously a proper threadlock might be better but they go off quickly and are useless next time you need them.
This is the cheap answer if you have a rubbery contact solvent type glue in your workshop. Obviously if you have to buy something buy the proper stuff- we have discount suppliers of threadlock at UK model engineering shows.