Midwayusa has the Bertram brass, about $35 per 20.
No one seems to sell bullets in .446, but a number of cast bullets in .451-452 are available and could be sized down .
The first thing to do is slug the barrel and see what size you really need.
Cast bullets usually shoot better if they are .001-.003" oversize.
A listed load for the .43 mauser is 30-33gr IMR 4198, of course ,start out on the low side. Since it is very similar to the .45-70, likely most .45-70 trapdoor loads would be fine.
Mountain molds is supposed to make custom molds for about $50 and up.
You might explore their web site.
The original bullet weight was about 375gr.
Lee makes custom sizer dies for $25 , just use them in your regular press.