I don't think glucose tablets are available on prescription as they're not medication. Hypostop gel is available, I think, but it's ruddy horrible.
If you're looking for discreet, I would recommend just the regular glucose tablets you can buy anywhere....or even fruit pastilles, gums, softmints etc. - anything that comes in a small packet that's just sugar. Personally I use Glucotabs - I buy them in bulk from Amazon - £15 for 300, which covers me theoretically for 100 hypos. I then just refill one of the Glucotab tubes whenever I have to. They don't melt in your pocket and they don't make mess everywhere - plus, while they're edible, they're not enjoyable enough that you'd overtreat your hypo with them.