Alprostadil dry sterile powder is not available for purchase in any chemists or pharmacies. This can be gotten from a doctor and it has to be prescribed. The Sterile Powder contains alprostadil as the naturally occurring form of prostaglandin. Contact your doctor for details.
Uhh... Not sure, but maybe, just maybe a pharmacy would carry it. Unless you already checked. If you're a doctor, which it looks like you are, you could ask the pharmacy if they carry it and show them an ID or something.