I grow the Viking cultivar and it's got a modest sweet taste to it. I wouldn't say they're bitter but they are quite astringent. To me it feels like all the saliva in my mouth runs away when I eat one. Kinda like a tongue puckering sensation. But it's more of a sensation, not a flavor. Their flavor is okayish.
They're great in jelly and wine and extremely good for you.
As for sourcing plants, I'd look around for reforestation or spring bare root plant suppliers for native plant establishment. Lots of places sell native plants for wildlife habitat and aronia are sometimes in the mix. Here's a place in Minnesota with them:
Honeyberry USA