Greg Field
Brian UKInner plugs are almost $43 each from Guzzi. In a pinch, you can use the commonly available CR8EIX plug. The only difference is that the tip is about 1mm recessed on the CR8EIX.
In the UK, the dealers charge £13 each for the inner plugs, which would equate to around $20.
I can buy them online here for about £22 a pair, delivered. The DCR8EIX works out at £15 delivered.
It is listed as the nearest equivalent, but has an Iridium center electrode instead of Platinum.