Sure it happens. Not very common though.
Most by people are far better off buying something from a bonsai nursery.
Lots of cheap material available that will look better then what most people can get out of landscape material for a similar price.
Many garden centers also sell some bonsai actually.
And to make a good bonsai out of nursery stock you do need some knowledge, especially in picking the right stock.
With the availability on hand it’s pretty much a waste of time to look for some landscape stock to transfer. I don’t bother.
I totally agree. With the exception of azaleas, gardenias and small black pines, most species suited for bonsai are not really found at home centers.
That, and most decent stock is much cheaper here than I imagine it is in the US/elsewhere (my local nursery has itoigawa shinpaku from 500yen for a two or three year plant from cuttings to 4000yen for something pretty twisted up and aged. Chuuhin sized.) -This only being true for Japanese species obviously.
That being said, I get most of my stuff from yahoo auctions/mercari. I got a nice shohin sized ezo spruce recently for 2000yen shipped and have gotten other trees for quite cheap too. I've got some really twisted up shohin kishuu shinpakus for 700yen/each from a lad on mercari recently. I find anything that can still be considered "unfinished" can be found very reasonably.
I did buy some larches from a commercial tree nursery, but they're poker straight and destined for a forest planting. I always look at home centers, but rarely find anything good.