Hopefully i'm wrong but i doubt you'll find the flanges 'on the shelf' in aluminium in that size anywhere. If you google eaton v-band flange you'll get a pdf catalogue with material and size options along with drawings & dimensions. Flanges, including aluminium, are towards the bottom. I know there's bound to be a few exceptions but commercially available 'easy clean' dry sump tanks are usually spun and the flanges for the band clamp are formed rather than machined and welded on. For example