They are illegal to buy without a prescription in the U.S., correct?
If you are concerned and want a prescription for Doxycycline, just ask your doctor for one. If they resist...play on their guilt:
"Oh c'mon, doc, I know you have cipro samples for yourself. The least you can do is write me an Rx to put my mind at ease. You know that Doxycycline is harmless, cheap, and a good prophylaxis for anthrax and plague. How about writing an Rx for me. I'll probably never take it, but it will at least let me sleep at night."
Any kind of doc can write for this, i.e., MD's, dentists (they prescribe it for gum disease all the time, they should have no problem Rx'ing this), podiatrists. Ask for a two month supply per person. That's equal to 120 Doxycycline 100 mg tablets per person. Don't take it unless you have good reason to believe there has been a release. But get the prescription filled so you have it on the shelf.