So I'm running a homebrew setting that is very low magic in general. Common people have no magic, though the ruling class are sorcerers. Divine magic is possessed only by a select few miracle workers/messiah types, as the gods are quite distant.
Enter the PCs, who are free to play any class. No one chose to play a healer, so I must find a (hopefully un-cheesy) way to get them healed. Also magic items may be difficult to justify being found.
Any thoughts on how I can keep the low-magic concept but maybe get some magic items in there once we get past the first few levels? The obvious is lost civilizations or alien/foreign invasion or travel..
What you need is Evil Lincoln's Strain Injury Rules.
The long and the short of it is that most hp damage just refreshes after an encounter. The only hp damage that doesn't refresh are "wounds" that are caused by crits or failed saves. Basically when the system says something spectacularly bad has happened, that damage is a real wound, and anything else is just bumps and scratches that you shake off after the fight.
This has two major upsides. It negates the need for minor HP management. No wands of cure light wounds, no topping off after a fight (unless things went really badly). The other upside is that every crit or failed save feels more dramatic. They are the moments that could make or break you.
Its a great way of dealing with HP. Better than the vitality system of star wars/unearthed arcana. AND you don't really have to change anything on your character sheet, AT ALL. Well almost anyway, just your injury points.
Low magic is always harder than it sounds. Just look at fighting a low-level undead without at least a +1 weapon.
What I would do is amp up natural healing a bit with some extra points for favorable circumstances. For example, healing an extra point of damage per level for a comfortable bed, another one for being tended 24/7 by a healer or nurse, another one for adequate food and drink, etc.
Space encounters out more often and only have wandering monsters attack rarely. If the party can rest between encounters, it greatly increases their resources and survivability.
The PCs can find some magical moss or spring water that act as potions of Cure Light Wounds when drank or eaten, but loses effectiveness if taken away from the site. That way, they can have a place to get back hit points quickly, but preserves the low-magic feel by making magical healing rare.
Another option is to have some mysterious magical creatures like fey take a liking to the party for a strange reason and give them healing potions as gifts.
Encourage one the PCs to take a cleric or paladin class by having one of the gods speak directly to him (even though nobody else can hear it). You indicated such things are rare in your world so the PC would be that one in a million. This may make taking such a class more attractive to the player.
Another low-magic threat you can add are infections from wounds. If wounds are not treated with a Heal check right away, roll for Filth Fever as if bitten by a giant rat, with a +1 to the DC for every 1/4 hit points left untreated. This may add some gritty realism you maybe seeking.
with regards to item distribution, etc. In low magic campaigns magic items are rare artifacts with histories and purposes. If you are going to make them rare, put extra work into them to make them memorable. Avoid minor magic items (unless they are evocative) or items that only provide bonuses (as they only really refer to the system itself, whch can be less evocative. Which sounds more like a real magic item, a "+5 longsword," or "flame-tongue")
It may take some reskinning but even with a magic item like a cloak of resistance, the less you mention to bonus value, the less it feels like commodity, or something to compare for its value. So less "well we have a resist cloak +3, but here is a cloak +4. We'll sell the old one ..."
Write histories for things like resist cloaks. Give them character, perhaps they also have skill bonuses or minor quirks. Maybe a penalty to something based on how it was used. All in all if there are going to be less items, each item is character unto itself.
If they think they can survive without a cleric, then let them try. It is more difficult, but it is possible.