UW142 lists a few 'known' submersion tasks. Are there any others out there that have already been dreamed up and documented enough to use here?

None of the lists tasks feel 'interesting' to my dronomancer TM for the initial submersion. Well maybe Reassembling, if the GM wants to have free sprites, and likely resonance bonds added in, but no resonance bond quality currently. For later grades, resonance realm search could work, but that is out for the initial round.

that's a shame that you don't have access to a free sprite... resonance bonds or at the very least free sprite contacts are imo one of the best investments a technomancer can make (you can gain sprite powers: how awesome is that???). and there are few submersion tasks so readily doable as feeding your registered sprites to a free sprite, not to mention a free sprite is an excellent ally to have in general (particularly when you can pay them in registered sprites for low-risk but high-value assistance).

the second best investment you can make, imo, is a technomancer network contact... either a party or guild (each has advantages and disadvantages, of course). i'm hoping you have access to one, and hopefully if you do, that one of the people in said network could hook you up with a free sprite contact.

failing that... well, you're a dronomancer. maybe you could create a unique machine, and the code for it.

alternately, i'd suggest looking at some of the initiation tasks to get ideas.

(oh, and also... resonance realm search is actually possible, you just have to find someone who can help you out with it, or manage to figure out how to be in the right place at the right time... there is a free sprite power called "resonance rift" which could get you there, or you can try to find a naturally occurring one, although that will take some luck as well as some knowledge)