For the brine shrimp and phyto - culturing your own is ideal (it gives you a stable, constant supply that doesn't break the bank), but that may feel too overwhelming at the moment in addition to trying to rear hermit larvae, and you can make do with buying as needed (the phyto is much harder to come by in a pinch than the brine shrimp for these purposes).
If you don't want to try culturing them, then you can buy a thing of brine shrimp eggs and just add enough per day to the tank to feed each hermit larva when the brine shrimp eggs hatch (honestly, you probably wouldn't even need 2 oz for a single batch of hermit larvae if you have a decent hatch rate).
[Ideally, you'd hatch the eggs out of the tank, remove the shells, and add just the nauplii, which you can do in a number of ways (with a hatchery, a net/sieve, or by decapsulating the eggs before adding them), but that is an extra step which I would honestly ignore if it makes the attempt feel more daunting at the moment. You can always worry about this with future attempts.]
I would however, recommend culturing your own phyto regardless of if you want to culture the brine shrimp. Isochrysis would be ideal, but it's notoriously difficult to culture. So, instead, you may want to go with something like Tetraselmis, which should be much easier to culture. If you have somewhere that stays warm and gets plenty of sunlight, you wouldn't need a light for the phyto culture; if you don't have somewhere like that for it, then you would need a light (you can absolutely get a cheap light for this, you definitely do not need a fancy reef light).
For the eggs:
https://www.brineshrimpdirect.com/brine-shrimp-eggs/This place also sells stuff like hatcheries, nets/sieves, etc.
For the phyto:
https://www.holdfastaq.com/store/p/tet-liveAmazon product ASIN B07MYDJBXJ(Amazon links often don't work on here anymore, so if this link doesn't work, it's Mercer of Montana 16 oz Tetraselmis [~500 ml]).
For the food once they're ready to start settling, I'd recommend TDO Chromaboost (probably the X-Small, but possibly Small, depending on the size of the hermits).
For the shells - again, this is the hard part. I don't know how big the hermit you're working with (
Clibanarius tricolor) is at it's megalopa stage (the stage it goes to settle at), but looking at other species in the genus, I'd expect them to be around 1-3 mm at the time of settlement. The only place I can find that sells Cerithium (or similar) shells that might work for that size is Cinquantagefleur's ebay shop:
https://www.ebay.com/itm/3747226334...Rn6xEkj-VWFcFDWUEFkot8-hjrATLDOB7SGj28ZSa_bMUThey also have these shells available in a wide variety of sizes, so you should be able to get ones that are appropriately sized for the hermit to transition into in their shop as well - I expect you'd need ~1/8"-1/4" (~3-6 mm) shells to start, then ~1/4"-1/2" (~6-12mm), then 1/2"-1" to finish out their growth. I doubt you'd need larger than 1" shells, but you can find larger if needed.
https://www.ebay.com/sch/i.html?_dk...e_name=cinquantagefleur&_oac=1&_nkw=cerithium
