Greenhouse roof vent frame

Trying to find  roof vent frame for a 8 x 6 europa manor greenhouse if anyone can point me in the right direction, Even one that I can alter to fit will do. I have just bought one off my association they had knocking about but it has no roof vent or opening windows and don't fancy all that heat in there in mid summer. Have spent a few hours on google looking but nothing that looks suitable. Going to try the one from my other greenhouse tomorrow but the trouble with that is even if it fits I don't know who made it !

cheers   

Its the fitment at the top were it slides along the ridge that I this is induvial to the make of greenhouse, have tried 2 this morning and neither fit. Your right the glass in most greenhouses fairly standard, if I cant get one I will have make one of the roof glasses slide down with some sort of stopper.

cheers

Will get one later on today forgot this morning as we left so the person on the other half of the plot could get on as he is well behind and we cant really keep to the 2m rule (plot was split) plus he is in a high risk job so better to be safe.

Its a 3/4 round and I think its a "T" fitment that slides in. My other greenhouse vent is a "T" but was too big to slot in.

cheers