Well, that carb would be a Marvel Schebler Carb.. sooo
In the TC-26E Parts Catalog
on the Cub Manual Server
, the Carb is shown on Page 26
and the Part Numbers are on Page 27
If you A is Gas only then it is the Marvel Schebler TSX-157 (I just re-built one), IH Part # 10.2657 and if it is a Zenith (optional) it would be 52499DB.
I would first get hold of say Ken Updike at Carter & Grunewald
, or you local CaseIH Dealer. They should be able to find the carb for you.
You can also contact Jamie at JP Tractor Salvage
, as they may have used Carbs for your A.
Hope that helps a bit...