Where to find provisioning materials?

I've started working on the provisioning skill, but I'm baffled by the vast variety of materials involved. Where does one find them? OK, game, meat and fish can be procured by hunting and fishing, and lower-grade materials such rye can be found, in tiny quantities, by searching boxes and barrels in dungeons and abandoned sites, but that hardly seems very practical. And what about the huge number of materials, for instance honey. which are simply not available to be gathered in nature?

You can also find food in inns, NPC's kitchens (there are always nicely stocked kitchens in castles like in Wayrest, Glenumbra, Mournhold bank, Kragenmoor, etc.), city docks and boats and delves with NPCs, like Ilessan Tower. Investing in hirelings on several characters is a good idea too, on max lvl you get 20 parcels of 2 ingredients plus a chance for several purple ingredients every 12 hours.
Vile Manse is a good grind spot if you don't feel like looking around the world. You loot the kitchen, go out the door and back in again.

well heres what me and Tessa do,

Step 1. Initiate a breach and clear on the nearest Delve (black hawk helicopter optional)
Step 2. Seek and destroy all lifeforms interned within with your Khajit Nightblade team :-
- Stab the healer
- Stab the Mage
- Stab the Archer
- Stab the Warrior
- Stab the Dog

Step 3. Stab.Open.Loot every single Chest, box, sack, small urn, barrel, trunk, rack and npc that you find, if its not nailed down take it, if it is nailed down, Take the nails writs are expensive and you'll need the metal

Step 4. Leave your calling card of choice (empty skooma bottles, severed heads, Horker loaf etc) and flee into the night with your bags filled to bursting

TL:DR - Delves are a great source of Provisioning materials that don't require laundering, literally tons of crates and sacks full of rye and lemons etc ready to be looted, Talos have mercy on you if you don't have craft bag or a huge inventory.