The recommendation in another Volvo forum is to get a used 940/740 rear door hinge that will be considerably less used and swap the spring out of it. Apparently it's not hard to do. Although the hinges are different left/right, they're the same back/front. The springs are apparently all the same.

My part lookup says the left door spring hinge is p/n 9447268 (item 6 in the fiche), a slightly different p/n from the 9244768 you mention. NLA, of course. Fitment is as you note, 700/900 and 90 series for the left lower hinge.

If the spring (staple as it's sometimes called)) was interchangeable with the 240 ones then I imagine someone would have noted it somewhere by now, but it would certainly be interesting to find a 240 and measure the spring profile as the Volvo engineers could easily have used the same spring. Having said that, the 240 spring kit you found from Swedish Car Parts in Illinois as their p/n 1355200-S is prohibitively expensive at $45 for just one little spring.

My springs aren't noticeably worn, but may be getting weaker with age and the hinge roller detent notches are getting a bit shallow and the rollers are a bit wobbly on their shaft. I always keep them well greased so they now barely hold the driver door open on an uphill slope. I used to occasionally grease the trunk hinges just like dealer service did when I had sedans. Those can be a bit tricky to get to. I should remember to grease my tailgate hinges one of these days.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now