Seems they have now finally integrated the Buy A Reward Flights (their words not mine) away from the Avios Webpage into aerlingus.com !

Either via the AerClub part of the website here: Buy a Reward Flight - Aer Lingus or via this interface: https://rewards.aerlingus.com/

Still not really easy to find availability over a longer period as it's still only showing a few days before/after the date entered but at least it looks better and easier to use than the Avios page.