I did a quick web search and came across this link:
http://www.mgcars.org.uk/news/news137a.html
It mentions a 1/24th scale model of an MGB-GT from a company called South Eastern Finecast for about 90quid.
It also mentions that it's the only known large-scale model of the GT.
Hope this helps.
I have a Corgi model of a(n) MGB Roadster on my desk (similar to the one I used to own in my '20s when I and two pals (each with a GT) used to crawl the pubs of our local brewery in sussex back in the day...) Shame Corgi didn't do an MGB GT
Good luck with your hunt.
David.