US maps on Garmin ?

Hi, bought a Garmin Nuvi a year ago or so with Europe maps on it, now traveling to US , and was hoping I could download the US maps on to it. I have been searching the internet for a while and I find the Garmin site especially unhelpful in this regard. It gives you the European updates and POIs etc, but not other GEOs maps. It teases you with all the maps they have and which you can view online, but I can't find anywhere how to download these to my device. I googled and found some sites where people have created their own map uploaders etc, but I was really hoping you could just download a map of Garmin's website for a bit of money. Has anybody figured this out, or is it just me, not being able to find this information ?

US maps are too large to download afaik, you need to get them on an SD card.

You mean get them on a SD card as buy them on a SD card ? Or download them to a SD card ? If buy them on SD card, you know where ?