The US Postal Service DOES issue international money orders in UK pound sterling. This service is not available at all us post offices but generally is available at the larger "full service" regional centers.
The cost is low compared to full service bank. The service is slow.
International MO are a hassle for the buyer and the seller. The buyer buys a Money Order voucher and gets a receipt for it. The buyer sends a copy of the receipt to the seller who has to wait for the MO to come from the US. The voucher is forwarded to the national service center in St. Louis (last time I tried) and a payment is sent to the seller 3-8 weeks after the money order voucher was purchased.
To the inexperienced, the process provokes the "scam" reaction. This reaction is unwarranted. In due time, the payment is made and the item purchased can be shipped to the buyer.
Because of the delays I prefer transacting with Pay-Pal and/or credit card. International transactions are where PayPal and Credit Card firms really shine. The buy and seller are shielded from the monetary conversion headaches.
Some businesses will only accept wire transfers and that is an aspect of international banking that I haven't figured out yet.
Regards,
Todd Teachout
Hercules, CA