There will be same parts shared on Partner saws from the same vintage (these come from an era when Electrolux swallowed up Partner/Poulan and Pioneer and are a Partner based saw). Possibly the caps off of Husqvarna 40-45's will fit, I will have to brave -3 to go find out- stay tuned.
Edit: Husqvarna 40 do not fit (fuel cap) of a Jonsered 2045- but Husqvarna 45 do and the 2045 is basically the same as a 2050. Should be much easier to find scrap parts saw Husqvarna 45's.