Really depends on whether it is mechanical or appearance parts.
I can get most mechanical parts over night from O'Reilly's.
Appearance parts have ben available through auto salvage yards. Spaulding Auto in Spokane has good selection. (800 366-2070) They have some after market body parts.
Yes, Sidekicks are different then GV in towing. There is a little weight difference. Biggest I notice is the front suspension. The GV has updated from Sidekick which was a big update from the Samari.
What parts are you looking for?
Front seal should be available from a good bearing shop. It would not be a Suzuki parts but replaced via numbers and dimensions.