The Minnesot Department of Administration has a public parking page.This includes a map with accessible parking locations noted.
Additional parking information is available on the directions and parking page of the Minnesota State Capitol website from the Minnesota Historical Society. The accessibility page of the Capitol website has links to accessible parking information and maps.
Keep in mind that parking is very limited during the legislative session (January-May). You may want to consider public transportation. Both the Metro Transit bus line and the Green Line light rail have stops near the Capitol.
There is a video offering parking options from the Minnesota Senate Media Services, which can also give you some pointers.