Unfortunately we do not carry spare parts such as the water inlet screen for that machine. You could contact Briggs & Stratton directly at (800) 743-4115 or check your local hardware store to purchase a water inlet screen. As for a gutter cleaning wand, this is a great tool for blowing out leaves and would definitely speed up the process. Also, your 1800 psi machine with a gutter cleaner attachment would definitely be able to clean your gutters with ease.
However, this Karcher gutter cleaner attachment would NOT be compatible with your Briggs & Stratton model 20358. Karcher attachments are only compatible with Karcher electric pressure washers. I am posting a link below to a gutter cleaning attachment that would be compatible with your pressure washer. See below:
PowerWasher Gutter Cleaner Attachment