The switches mount into plastic 'pop-out' panels in the dash, so no, you don't have to remove the dash. Just use a wide flathead or narrow putty knife blade to carefully pry them out. You might need to reach around the back & squeeze the clips, but they should pop out from the front.
Assuming you mean the rear defrost on/off switch just below the mirror switch?
As for sources I'd probably try a pick-a-part first, but then you never know what you'll find.
If you want to go new check megazip for the part number & then do a search.
https://www.megazip.net/zapchasti-dlya-avtomobilej/suzuki/sidekick-sport-8589/sv418-18300/sv418-my-96-98-sv418-327270I've used megazip for a few parts & had good luck, but be aware: I have found some parts mixed up between SV418 & SE416. In your case I think the switches will be the same anyway so it won't matter. Just be aware they are international & the Sidekick Sport we got in the US isn't necessarily exactly the same as other market SV418's.
In any case, you can find the part numbers there & search around... maybe eBay would have those switches & for a lot less than OEM prices. Hth.