Desperate for help re: Rangemaster sink with Inskinkerator

[Secretsout]

Hi experts, looking for some help. Our new kitchen is having the final touches put in today and we've come across a problem. I'd ordered the wrong size sink so for an urgent remedy I accepted what was on offer from the supplier. So we have a Rangemaster QUB3416L. We also have an Insinkerator to use with is. Here is the sink. www.tapsuk.com/rangemaster-atlantic-quad-15-brushed-stainless-undermount-kitchen-sink-qub3416l-p8900. Problem is, the plumber has come to connect everything as the worktops have been fitted and it turns out that the Insinkerator does not have an attachment for a square waste! Cue a frantic call to the sink supplier who assure me the sink is compatible with the waste unit. They call Rangemaster to check and it turns out they do have a part but it's £99 and they can't get it until September.

So my question is.....anyone know where I can source the part quicker. I've done a fair bit of googling and can't find it. Insinkerator themselves are no help. Desperate to get it sorted as I'd prefer not to wait until September to have the Insinkerator plumbed in.