Windows with nail flange in UK?

[Danelectro]

Got plans to box off veranda area at back of ground floor flat.

The main side wall will be Timber framed/stud, OSB,House Wrap and Larch cladding.

Joiner will do the framing and OSB but I'm installing the house wrap and cladding and also one large window max 750 x 1500 (may have to be epress?) and possibly a strip of 3 glass blocks if I can figure out how to install.

Can find plenty made to measure uPVC at good price but nobody seems to have with nail flange.Anyone know who makes nail flange windows at a good price in uk or is there an easy way to fit without flange.

Cheers