Yip almost any seats will fit usually quite easily getting front singles is not easy nor cheap due to the fact most were captains seats and very desirable therefore expensive 
My last T4 had Fiat Brava seats in it and my current one has Merc 190 seats [very comfortable btw] both of which have or were fitted to swivel bases very handy to turn seats around to face rear 
Chas has leather Rover 75 seats in his T4 2 front and 2 rear[very comfy] and i am sure there is a guide to fitting them and Rover ZR seats somewhere here-in, the only issue with fitting is the height from the steering wheel, proximity to the handbrake and will require new mounting holes in your seat bases ....... [just need plated and new holes usually to take new runners]
Just about every friont seat has been retro fitted to a T4 at some point or another by somebody when you can buy them so cheap in scrapyards against T4 captains seats it starts to make sense
