There are after market bogie and pony wheels available in N gauge, your best bet might be trying the N Gauge Society www.ngaugesociety.com to track 'em down.
For couplings one solution might be to use Fleischmann "Profi" couplings, part number 9540 is a straight replacement for the standard N gauge coupler.
60134
For couplings one solution might be to use Fleischmann "Profi" couplings, part number 9540 is a straight replacement for the standard N gauge coupler.
60134