Understood. Well... if it is simply a matter of replacement then you can just buy a suitable new roller and then bolt it on making sure you use the existing backing plates or having new ones fabricated.
Here's some roller specs...the CRM-1 looks like the appropriate one for you.
http://www.windline.com/diagram.html
We had a custom dual roller arrangement mounted to a stainless steel plate with appropriate backing fabricated for our Irwin44 some years ago and it set us back a couple of grand so using stock stuff if suitable is the way to go.