I would call Tom Papadopoulos in person..Most educated AM guy in north east.. He always has a line on one and has a few in stock as well https://www.autosportdesigns.com/vehicles/current
Assuming you are looking in all the usual places? https://davidsclassiccars.com/aston-martin/550155-1977-aston-martin-v8-vantage.html Why just 77-78 model years?
Got it! Honestly, I would consider the advice above and call Tom at AutoSport. If nothing else, you may find some additional information on these particular models...
And, did that work out OK? Tom had my 550 on consignment prior to my purchase. Seemed like it was represented well at that time...