Unreal, I'm literally having the exact same problem with a '10 Sequoia I just bought, can't get it passed safety to register it because of a broken rear spring. Impossible to find 3rd party, Dobi's regular height are out of stock, I don't want to lift. A couple questions if you don't mind:
1. I'm finding the stock rear springs are VERY expensive because they're discontinued. $426CAD each. Where did you get your springs and how much did you pay?
2. Is it a must to change the shocks at the same time?
3. I'm in the same boat with respect to towing, I've got a smallish travel trailer (5000lb, 22ft) and don't want rear sag. Is that why you got the spacers? Which ones did you get and where did you get them from? Are you happy with the ones you got, would you recommend them?