Hi. I am in process of replacing that window too.
I just ordered a MayGood MG17RW a couple of weeks ago on Amazon($500)
It is a 900mm x 500mm push out window with a frame (***Link Removed***
The opening of the Lance830 is 890mm x 510mm so I maybe will need to do some shiming.
I should receive it by Thanksgiving. I will keep you guys updated if it worked or not (If it does, I will need to do it for the other side, so it matches ...).
If not, maybe we could get all together to order on Alibaba if there is a MOQ for a 900mmx520mm frameless (there is a MaygGood MG17RW-WF that is frameless, but I did not find anywhere else than Alibaba)