I have just been looking at the latest newsletter from Opel GT Source, a long established company based in California, USA, who specialise in parts for the Opel GT, Opel Kadett B series and Opel Manta A series.
I was pleased to see that they are selling some very nice reproduction parts, such as the following:

• Original “Early Style” Shifter Knobs for original 4-speed Opel shifters, & a 5-speed design is also available, these are priced at $25/each.
• Opel GT Armrests offered in black as a reproduction item for original Opel GT interiors, these are priced at $50/each
• Opel GT Poly Suspension Bushings in a black finish as a reproduction item for front control arms and rear trailing arms. These are priced very modestly at $35/front suspension set of 8 (order as #3026-B or #3027-B) and $75/rear suspension set (order as #3025-B).

Opel GT