Firebird made this and the Windjammer, back around 85 or so, it shipped with a 6BQ5, there was 2 styles of tuning arrangements for it. One had a ferrite core inside the cardboard formed coil, tuned with a small alignment type tool which came with it. The other style had a large finger ring formed from a plastic coated rod with some ferrite on the end of it, you moved the tuning rod in and out.
You won't be able to find replacements anywhere, much like its counter-part on the BlackCat JB series, they were custom done, and difficult to obtain even when they were actually being made. Best bet is to take it to someone knowledgable enough to make a replacement that will work.