The 3 day for the price of 2 ticket is not available on the English disneyland paris website but is available on the French website (though we need a French address/telephone no). 365Tickets does offer this option and seems a better and a cheaper alternative to UK website which is £144 (another rip off for UK residents). The site also offers a 3% quidco cashback. I understand you get a voucher and you change it for the tickets in Disneyland Paris.
Disneyland® Paris - 3 Days for 2 Party Pass
Special Offer 3 Days for the Price of 2!
This Disneyland® Paris voucher provides admission to both Disneyland® Park and Walt Disney Studios® Park for 3 days for the price of 2 days (not necessarily consecutive). This voucher is valid for both Disney® Parks within the same day, subject to Disney® Parks capacity on days of visit.
Includes FASTPASS - a great way to experience the most popular rides without queuing.
The Party ticket voucher can be exchanged against the corresponding Party ticket within a 6-month period from the date of purchase. The ticket given in exchange is valid for 3 days within a period of 7 days starting on date of first visit.
*Tickets bought in this sale are valid for 6 months