Wacom replacement nibs are actually hard to find at reasonable prices in Canada.
For one, most of the dealers are in the US, so there’s really high shipping costs.
Anyway, I’ve found one of the best places to buy wacom tablet nibs is DIRECTCANADA. The secret to buying there is BUY OVER $50 OF GOODS AND YOU GET FREE SHIPPING.
So for example, here I’ve filled my cart with $50.09 of nibs. Magically, the shipping cost goes down from $20 to $0.00.
The best nibs for the 12WX and 21UX (the pens that come with both of those devices use the same nibs) are:
Very soft nibs (black) PSIA043
Harder white nibs ACK20003
see on Wacom site