Do you know of any squishes that are a geometric shape, like a cube or sphere?
Yes-ish for shapes like spheres and squares - as long as you’re not after perfect geometric shapes. (Otherwise, it’s a flat no, sadly.) Most rounded squishies have one flattish side, or, if a fruit squishy, a stem. As for triangles, pyramids, cubes and other more interesting shapes, a flat no.
It might be worth your while (if you have time on your hands) to check out the remnants in the stress ball section at Office Playground and see if any (actually left in stock!) have slow rising or similar in their description. I used to have a stress ball from a tourist shop in Queensland that’s pretty identical to a squishy in terms of how you could compress the ball and watch it rise (it was awesome so of course I lost it). I looked at Sensory University and Fidget Club and couldn’t find anything; I’m going to have to do some digging to find a new general-office-toy supplier to fill the hole Office Playground is leaving, especially for things like stress balls. I tried searching Banggood, but I couldn’t find what I was looking for in their listings.
All I can say, less helpfully, is that slow-rising squishy-like stress balls do exist and may fit your spherical needs better. If you can access dollar shops, it may be worthwhile keeping an eye out.
As for squishies, see below! I’m browsing Banggood because it’s easier to search and the links are permanent (unlike ebay listings) but I suspect that if you copy and paste the item title into ebay, you’ll find it there, too.
(All Banggood links are listed in AUD, as what’s displayed for me; check each link for your own regional pricing. Most items offer free international standard shipping.)
The marshmallow ($3.44 AUD) and panda squishies ($3.24 AUD), whilst technically food, look least like food and do have one flattish side. These steamed buns ($4.37 AUD for five) also have a flat side, but it looks a little less flat than the others (although this may be photographic illusion).
A pomegranate squishy(on sale at $7.16 AUD) is perfectly round but has a stem. There’s other round-ish squishies like the apples ($3.31 AUD), but the pomegranate looks most spherical, save for the stem, to me.
(I also don’t think much of the quality of the apple ones in that listing, personally, so I’d try the pomegranate first, as it’s a brand-name and likely higher-quality item, if you can afford a few more dollars on a squishy.)
If you don’t mind a hockey puck/disc shape, the black rice steamed bun ($1.83 AUD) is as close to a perfect geometric shape that I’ve found.
If you don’t mind round and egg shaped, the egg yolk squishy ($3.97 AUD) could be perfect. Likewise, these Easter egg squishes ($3.31 AUD, currently awaiting restock). They’re also available on ebay for $3 AUD or $2.25 USD, free shipping, if you think the egg shape works and want traditional-squishy texture.
I couldn’t find this toy on Banggood, but it’s available on ebay at various prices and is a flat square shape with the exception of the strap anchor, feet and ears: tofu squishies. (Link to search on ebay.au.) I think it’s as close to a full cube as you’re likely to get. (It’s shorter than it is wide, hence not a proper cube.) It’s fun to squish, although a little too sweet-scented. These ones are $1.56 USD with free shipping!
I looked at SillySquishies, and while also being much more expensive, the only things that might fit your requirements are the Animal Buns ($10.40 USD) and I cannot confirm they don’t have a flat side like all the other buns linked here. They look as though they’re least likely to have one, but one photo makes it difficult to tell.
I didn’t find anything I thought suitable at Modes4u, but their squishy range is amazing (check all the subcategories on the left-hand sidebar; the food squishies are incredible) and they too offer free international shipping. They did have vaguely-round-ish-spherical shapes in some food and character squishies, but less close to the brief, I think, than Banggood’s offerings. But if you’re after higher-quality squishies generally and have a little more money to spend, I think this is the place to look.
This is a lot of words to say not really, I know. If folk can help out, please let me know and I’ll post it!