PTI products are only available from their online store - unless you buy used, like from their For Sale or Trade forum.
Some people ask on the PTI forum for a shipping buddy. There are usually people in the US willing to receive your order, strip out the extra packaging (like the plastic boxes the stamp sets come in), and repackage and mail to you. There are quite a few overseas customers who get their PTI products this way. And if you are not ordering card stock, many things can be sent in a padded mailer instead of a box.
Others pair up with other customers in their country and split the shipping costs for an order.