Original wood would be quite difficult to find, but not impossible. The internet is your friend, there are a few makers of reproduction wood, but nobody with much of a catalogue to browse. Probably a one off by a stock maker would be the way to go, but $$$.
There are repop fore ends around for the 577/450 MH, your barrel is of slimmer profile, the larger barrel channel would need to be addressed.
Your existing wood looks to be solid, it could be repaired. A front section could be spliced onto your cut down fore arm with the joint hidden underneath the barrel band. Probably the easiest and most viable route and if done right, undetectable unless you strip the rifle.
The metal nose cap and barrel band can be found with a bit of time and effort.