48t and above mtb chainrings / road cranks on mtb (?)

was wondering where can you buy 48t, 50t (preferred) mtb chainrings locally?
104bcd for shimano deore-type cranks. know that blackspire makes some
but not sure if its available here.

also, has anyone frankensteined road CRs attached to a mtb BB?
is it even possible?

------------------------------------------------------------------------------

not really a spinner, and during a long-distance cycling events
(200km & 300km) was definitely wishing had much, much heavier
gears than the current 42t-11t during flats.