Are raids at all gyms?

No, they are only at some of the gyms. You will only be able to see the ones on the radar in the same kind of radius from you as pokestops on nearby.

At the moment they are only at sponsored gyms in your local area.

I saw them at Sprint stores and Starbucks in NYC. Others over seas like Japan saw them in McDonalds.

I've actually seen them at non-sponsored gyms now...maybe it was a bug since it was everywhere, but now, no where again...

Just came from one that was at a non sponsor stop. It happened to be at one that I needed to feed berries. Otherwise I wouldn't have know. I have been looking all day too. I was the only one there and no way to take down a 30k Rhydon

Went through town, saw one at a post office(said sponsored), and a restaurant. Not sure if the restaurant was sponsored.

I got 1 Raid pass this morning from the only gym accessible to me (5km away from home). And after 2 hours of walking, I saw a Raid Egg popped up. I was surprised because I didn't think we could get a Raid that quick, considered the size of my city. However, it required another 1 or 2 hours for the egg to hatch and I couldn't wait that long so I went home.

Now I'm on my way to neighboring city which has more gyms. Can't wait to join any Raids there :)

Cheers everyone. Wish you luck!

I had a raid pop up at a non-sponsored stop. Had to wait about 90 minutes from when I first saw the notification. Boss was a CP ~11,500 Magmar. Nobody else showed up, but I picked a team of Vaporeons and hydro pump Gyaradoses, and won without too much difficulty.

all started up at lunch time today for me some have a timer for 1630 hoping there will be a couple for after dinner when i can go for a walk

There was a huge rush of them around here a couple hours ago. Out of about 30 gyms in a 5-mile radius, at least 9 of them had raids going on at the same time, without even checking 1/3 of them. I can't believe they were all sponsored locations either, since most were at churches and cemeteries.

Little town in Finland

I'm in us, Wisconsin. Been seeing them all over today. Two in my town that only has four and a bigger town nearby that has about 25 gyms had 3 or 4 pending or active. At any given time. Oddly it did say "sponsored" in two gyms I did raids at even though they weren't at sponsored locations just random gyms. So maybe a bug? but was active as of an hour ago. I'm home now and can only see one gym from here and that one had a raid this morning​ so I wouldn't expect to see another there soon.