You can try your local commercial roofing supply – Look up Harvey, Bradco, Beacon or ABC roofing supply in your area, and find out if they will sell you what you need.

Usually these places sell only to contractors, but I saw them sell to the homeowners a few times – but of course at a premium price.

I actually do not think there is a seam tape 2″ wide – they come in 3″ and 6″ widths. You will also need rubber cleaner and primer to apply the seam tape. If they tell you that it is one in the same, find a cleaner somewhere else or use acetone or gasoline to clean seams before you apply the primer.

I do however recommend using cleaner instead of acetone/gas, as latter two are not made for cleaning rubber.

Good luck