Check your neighborhood/area for pool maintenance companies;
I once got a whole stack of heavy-duty 5-gallon plastic buckets from one of those places.

All you have to do is poke holes in the bottoms, & you can do that with a hammer & a big nail or an icepick.

Will all those chemicals damage the plants? I would thinking even cleaning out the buckets would still leave trace amounts of the chemicals.

I never have had a problem;

1. the buckets have little if any residue, they look clean as a whistle.

2. I swish soapy water around in them just for good measure.

3. organic matter tends to neutralize traces of bad stuff, according to what I read on the Soil Compost & Mulch Forum:
there are companies that actually use a composting process to de-toxify contaminated soil or material.

4. the plastic containers may involve more off-gassing than any traces of other chemicals (& we eat & drink from various forms of plastic all the time!).

5. you might want to use the buckets just for toting mulch & starting trees, & put your vegetables in other containers.

I have used them for years as we do our own chemicals in our pool, and I have never had a problem.