Some crazy prices on some of them for such a small and simple pump though, but we all know how tractor parts go in general.
Another option could be blanking off the spot for this OEM pump and mount a generic one at the front of the engine powered by the crankshaft. You could even go a slightly bigger size if you have a loader or backhoe to make it a little bit faster.
I bought one from www.whp.co.uk for £234.36 inc vat and delivery. I had the choice of one the same spec (pressure and GPM) or another the same size, but slightly greater GPM which I ran with.