Doxycyline for birds :
http://www.drsfostersmith.com/product/prod_display.cfm?c=5059+5992+25823&pcatid=25823
There’s always Petmeds
Last January (when I needed doxy) Foster and Smith were on backorder for it. It was in short supply everywhere (including Canadian pharmacies online). I ended up paying $2 per capsule from the vet (doxy is the drug of choice for treating Lyme and Heartworm so the demand is still there.)