Is this a Sweepy v1 or v2?
The v1 fits a 35mm fitting for a European dust extractor such as a Festool.
The v2 has two adapters, one for a 35mm fitting, the other is a cylinder which accepts a 2.5" hose and plugs in directly — it would be pretty easy to cut one on the machine out of a suitable material:
or you could make a form and cut and bend say a flexible cutting board and rivet it.
Probably a 2.5" hose coupler would work, you’d just need to get one intended to fit inside the hose — check in w/ places which carry dust collection gear (Lowe’s, Home Depot, Woodcraft, Rockler).
That said, I consider Sweepys a consumable item (hazard of cutting metal w/ dust collection running — clouds the plastic) — a new unit would have a new coupler: