Normally the skis have a sticker on the hull showing ultra low emissions. That’s what they might be looking for. Maybe you could get one reproduced? If they are looking by approved mfg/model/year you're probably out of luck if the ski hull is not one on the list of approved models. EPA certification is done by 3rd party testing labs and is only valid on the stock ski- putting an ultra low emission in a different hull means that that although the engine may produce the same emissions, if it wasn’t tested and certified, there is no guarantee that that it complies. Usually aftermarket companies have to get a certification independently when they modify any engine to prove that it hasn’t adversely affected the emissions. When they pass, they are given and OE number from the EPA.