I know Jerry Rutman did some upgrades for this kit, but sadly, he's closed up shop.
There's only 6 items that I know of for this kit...
MDC makes an engine for the 109 - www.modeldesignconstruction.com
Eduard makes an interior and exterior PE detail set, and a canopy mask set.
True Details does a resin cockpit set
Verlinden does an update set...it's basically all inclusive.
Hope that helps,
Jeff Herne
Modelwarships.com