This evening's feeding was rather traumatic. Maple has decided that he now hates any and all syringes, but for the first time we were actually able to get something into him. Mostly because I finally realized I was too timid and turned the syringe over to my mom. While sympathetic, Mom understands the "force" in "force-feeding," and she didn't let him get away. The new syringe also helped.
Speaking of the new syringe...y'all, we bought 13 syringes today. I think we might be crazy. However, it should be noted that 12 of those syringes came in a single pack, and we only got them because we thought they'd be the best thing we could find. Later, though, my wonderful and dedicated mother found an infant-feeding syringe of some sort at the pharmacy, and we were back in business. It's got a wide enough opening to easily let the goop through, as well as a long enough end to make feeding possible. And it holds two teaspoons, which is much more reasonable than 1 mL.
@spy9doc , I did try valiantly to find the small pet feeding syringe you suggested. But if it's supposed to be something I should be able to find at any pet store, you haven't met my pet store. The closest one is 45 minutes away, and...well, they're more cat and dog people there.
Speaking of things that I should be able to find and can't, we checked 4 1/2 stores and found no vitamin C supplement. All we could find were multivitamins, but I was fairly sure that wasn't what I was looking for. But we're going to the farther away and bigger city tomorrow, and we should be able to find something then. Also, besides that it was a very successful day. We found corn and spring mix and kale (he doesn't like that, apparently) and all the other things, and I got him some hard timothy-alfalfa blend hay cubes to chew on (he's not super into the one I gave him, but I know he can eat it because he ate an alfalfa-carrot version. I think it'll help him wear his teeth down, as well as get timothy into him when he can't eat it normally).
Tomorrow my boy is going back to the vet. Apparently they have to put him under anesthesia to look at his teeth, which makes me very uncomfortable, but I'm going to trust they know what they're doing. It'll be nice to actually meet this vet I've heard so much about. I'm hoping she'll show us how to do guinea pig PT.
Besides all that, there are four other updates:
1) It seems that he can't eat timothy hay because he can't get it at the right angle. So while he was eating his house today I plopped some soft, aromatic orchard grass in front of his face. Then I watched him eat it for what felt like ten minutes. It was a beautiful sight.
2) We've been weighing him every day for the last four days. Over the first three he was dropping steadily by degrees of about ten grams, but today he remained stable (by which I mean he went up 2 g, but that's not a significant amount). So that's good. Or at least not bad.
3) He is now pooping normally, although it's very small--more hamster-sized. Also seems like a good sign.
4) He's grooming now, which I hadn't seen him do for a while. And when I came into the room at feeding time last night, he wheeked loudly in greeting, a sound I haven't heard for I'm not sure how long. Also seems good.
We're praying for a safe vet appointment tomorrow. Thank you so much @bpatters for the suggestion of orchard grass! I never would have thought like that but it's working like a charm.