Sorted 22" GT Frame. 23"+ Marin frame.

[Tootyred]

The marins have big head tubes 180mm on the 20.5" if that helps. It depends why your looking for big really.

Earlier saracens are also pretty big too and the upper and were good quatity tubing.

 

[Spankyfart]

Found a 95? Indian Fire Trail in 20,5" 100,- euros, frame seems good.
At some point I'd still like a 22" GT frame but that's when something falls in my lap.
Got a nice project to work on for myself once (instead of fixing other peoples bikes )
Not much salvagable but a few nice parts, wheels are shoddy. Rim walls are banana shaped so there is more buying to do.

 

[kingoffootball]

https://www.retrobike.co.uk/threads/large-gt-frame.472100/