Hi Brian,
The part you need is number 400801, (complete balde carrier assembly). Tool is actually made by a Dutch company called Ferm and rebranded and sold under severl different names, so you may need to contact them to find this part if it is available. What I will advise though, is that the cost and hassle of getting this part would be not economical compared to the tool's value. I have done a brief search online for you and have found a second hand version of your saw for sale for less than £30 including delivery which would probably be easier than going down the repair route:
See following link:
https://www.cashconverters.co.uk/shop/product/saw-power-craft-prs-850-in-hard-case/369550
Obviously I can't vouch for this listing and it may have expired by the time you read it, but it won't be too hard to find a cheap used replacement tool similar to this.
Rupert, December 2019
