my shop doesn't carry them and i play them on my other guitar. but they don't seem to even make them for 7 strings......
Schecter Hellraiser C7 FR/Bareknuckle Cold Sweat/Liquifire
Godin A12 - For Sale
1991 EBMM Silhouette
Emperor 2x12

7+>6, ERG Legion

Like going fast?
Usually if you go to a luthier you can buy guitar strings for like $1.00 each. At least that's what my guy does.
I'd recommend just buying your choice set of 12's then a single B string.
Do you keep your guitar in standard tuning, or do you drop tune it like I'd assume you would with 12's?