There's loads that fit the force engines there's the hpi there's Hong nor , ansmann ,to name three and they all have week points the hpi it's the handle the Hong nor its sometimes the spring the ansmann it's the plastic case where the screws go are week.
I found ansmann ones to be cheapest and with washers on the screws the case holds up to most abuse
This is a basic one http://pages.ebay.com/link/?nav=item.view&alt=web&id=141393744445
Ansmann one http://pages.ebay.com/link/?nav=item.view&alt=web&id=321206589408
Force one http://pages.ebay.com/link/?nav=item.view&alt=web&id=400584891756
Hpi one http://pages.ebay.com/link/?nav=item.view&alt=web&id=310869151482
Take your pick but the one I would get is the basic one