Dennis type Z big end bearings

Hi, I'm new to the forum, I'm in the process of re commissioning a 1954 Dennis type Z to working condition, the owner told me the machine was checked and run up after he bought it but after 20 minutes the machine lost power then stopped.

The person running the machine came to the conclusion it had spun a bearing and returned it to the owner, I've now got the machine to diagnose and fix, I've stripped the engine and discovered that the big end bearings have failed, the white metal has parted company from the bronze shell either from corrosion or overheating.

The problem I'm having is sourcing a replacement pair of bearings either new or in usable condition, all places I've contacted either don't have any or in the case of having them re surfaced isn't a cost effective route to take.

It has crossed my mind to source another engine and harvest the bearings and crankshaft but even then its finding one that's cheep enough or isn't seized! 

Surely there must be a stock of bearings somewhere after all these machines were manufactured  and sold for a long time worldwide. Long story short, does anyone have a pair or can point me in the direction of somewhere that has? It's the only thing that's holding me up now. Many thanks.