Contact www.equipatron.com via email or phone. They have some great techs that can help you with a suggested replacement engine. Note that they are busy at this time of the year so be patient waiting for an answer. Email might be your best bet.
Honda...Subaru...
Briggs and Stratton makes pressure washers under their name as well as the Brute brand. Give them a look.
Also look for ones with AR pumps as Grainger and other have parts for them.