Belling Forum 500 - looking for replacement oven door seal

Recently bought a house, and it included this Belling Forum 500 cooker which I believe is from the early '90s. It mostly works fine (grill/top oven and one ring don't - I'll get to them later), but the oven door seal is quite bad - and I'm having trouble finding a suitable replacement as none of the parts shops online list this model and I can't find any parts reference for such an old model.

The seal is about 1620mm long. Any suggestions?

(cleaning is a work in progress!)