Best price I've found for Genuine Volvo parts is from Tascaparts.com - with that said Genuine Volvo carry the Volvo brand but most are manufactured by OEM suppliers. Sites like FCP Euro, IPD USA, EEUROPARTS will show which aftermarket suppliers are also OEM (meaning they sell to Volvo). You should replace the idler pulley and tensioner along with the timing belt - and probably do the serpentine belts as they need to come off and inspect the drive belt pulleys. As to the water pump, while it is true that the timing belt needs to come off to replace the pump, these are not common fail items but should you want to replace it, you can look at Aisin as an OEM brand water pump - get a kit with bolts and gasket and then plan on a drain/fill with fresh coolant.