I have a pack of Deryni Dice so I am covered.
Deryni Dice were a pack of 8 Fudge Dice, 4 black, 4 white.
They were manufactured by Crystal Caste and marketed by Grey Ghost (GGG9008DA)
Other alternatives would be purchasing blank dice and using permanent marker on them to at the +'s and -'s or using normal dice in the interim and and counting 1-2 as minus, 3-4 as "blank", and 5-6 as plus.