Can I just confirm the following please:
1) Homebrew games and apps are open source and freely distributed (and thus entirely legal to use and own).
2) Games stored on the card as downloaded roms are LEGAL if you physically own the actual cart anyway (so if you have 20 physically owned games, rather than carry 20 carts around, you can store all 20 on your R4).....
BUT it is
ILLEGAL to download and use roms of games that you
do not physically own (as mentioned in the OP).
Generally speaking, on a forum I assume that most questions about roms (no matter HOW MUCH someone insists that they own the games anyway

) is usually a round about way of them trying to discuss illegal piracy of games they don't really own.
So I think that we should assume
all "game rom" talk can be used in piracy and therefore we should not really discuss it here

.
Moving on to R4 shop stocks, the best place to get them from (I have bought about 4 for various rellies and friends) is from Dealextreme.com. They used to be a standalone company but they have since set up a sister site called Volumerate.com that deals mainly with retail outlets.
When you click on an R4/bundle, you're directed to the sister site (volumerate) where you simply specify 1 unit (as opposed to the 10 or 100 that shops will request).
They do bundles of 2Gb microSD cards (Sandisk or Kingston) with the R4 pack for a total of £30-35 ish all-in (depends on the dollar exchange rate on the day), and they are a US company but they ship from HK so it takes 5-10 days to arrive.
Every time I've used them I've had great service and am yet to find a cheaper UK alternative.
P.S. My biggest complaint about Amazon is that the marketplace sellers usually advertise low prices of £1-£2 but it's when you go to buy that you're informed that postage rates are £7-£10

. I HATE it when they do this.
I really wish Amazon had a search filter that allowed you to ONLY look for genuine "sold by Amazon UK" stuff .......if I wanted extortionate shipping fees I'd go to Ebay

.