Yes, a specialty bird feed store would be required. I don't think I have seen it elsewhere for sale. A Squirrel might try it but I guarantee it won't like it and eat anymore. Hopefully one won't have a temper tantrum over you putting safflower out.
Hi Rob'in'To,
Thanks for the tip, we've had some good results! Initially we eased them into the safflower by mixing with some sunflower. Now that we've gone full safflower, we've hardly seen the squirrels and the grackles lost interest too. Our cardinals are now back and feeding, and the other smaller birds go back and forth from the nyger to the safflower. Strangely enough a couple of grackles were still around, and a bonus they were chasing away the squirrels that did come by... we didn't understand why the grackles were still around and behaving like that until one day my husband noticed a grackle from the second floor window, and it was about 3 feet from the top of a blue spruce in our backyard. He got out the binocs and sure enough there was a nest.... so a few weeks later a couple of grackles are still around but not eating our seeds :-) I'm hoping they leave after the little ones are able to fly. They have made some good entertainment chasing a hawk that soars above and nipping at the squirrels. :-)
I still have quite a bit of the sunflower seeds, so maybe later in the summer I will try using some, or store it well and keep it for the winter.
Thanks again for your suggestions!
Mar