A lot of my drawings are 18 or 19x24 inches and I don't have a scanner for those. Though I know there are companies out there that can scan large artwork (much larger than mine) for a fee and you may need to ship it.
That being said, this is the scanner I use now. It fits 11x17 in drawings (which is the size I would like to work in from now on.) I've found that it does scan a little light, but can easily be corrected with any basic photo editing software, just adjust brightness/contrass/etc.. This particular scanner is out of sale (on amazon, anyway) but if you do plan on finding/ordering an A3 scanner, make sure that the scanner BED, the place where you will put your drawing/work, is actually A3. A lot of printers/scanner combos advertise A3, but it turns out the scanner is standard 8.5x11in and it prints in A3. It took me a long time to find the scanner I did, unfortunately.
If you aren't able to find a scanner to suit your needs (though if you are working small enough, you should be able to find one in a decent price range and even portable!(ish)) then you should look into researching how to photograph artwork. There's a special skill to it that involves lighting and tools and cameras... Nothing I'm very familiar with. I just mess around with my phone or other camera until I'm frustrated and give up. I do that for a few days before I settle on a mediocre photo.
I don't think I would recommend scanning oil paintings, though you may be able to safely if you do some research! Good luck and I hope this helps.