hahah!! welcome to the club! ^_^
the best place to find them is here, the mlptp and on ebay.
mercadolibre is an option but for me its too much trouble unless its a really rare argie . btw the prices are not in USD
baby posey and sparkler are pretty popular so they are at the more expensive end of argie babies with the blue haired sparkler being the most expensive (and most htf).
Ive never seen the one with orange symbols, do you have a link?
if you click on my sig I have price rages for all of my argies so you can see what to expect to pay for all these lil cuties
on a side note, sometimes it helps to have a wanted pic in your sig. i always get PMs from people who spot the ponies in my sig ^_^