I can't remember the manufacturer's name, but the company produce a range of cast, white metal after market accessories, including landing gear legs, guns, engines etc.
Have a look at the Hannant's web-site - select 1/48th scale, and 'P-38', and everything available should then be displayed. Having identified the manufacturer etc, you can then order them locally if available, or direct from Hannant's.
I recently found the advert for the P-38 set in a modelling magazine, as I was going to replace the legs on my model. But I've put the magazine somewhere safe .... so safe I can't find it !