Dyson Parts (online store)

I don't think they offer discounts on parts. Although I have seen them lowering price to clear the discontinued parts, but it wasn't worth much.
Having said that, if you call Dyson and register your products for warranty, I think they offer you 20% discounts on Dyson products (forgot what its called.. owner rewards?) but since you are a previous Dyson owner, they will give you 20% discounts on all future purchases. It should include parts & accessories because I purchased my Dyson V10 Dok with 20% off last year.
I always find it better to call Dyson rather than ordering it online. You may receive some new info while talking to the sales rep. For instance, the filters you are looking for may be back-ordered, and they can put you on the list to notify you when the filters are available.. some stuff like that..