My guess is that the powder coating is to blame, the extra paint on the wheel means that the centre bore is now slightly too small.
I'd also guess that the wheels are the correct PCD, however if they are not and you've blown money on powder coating and tyres without checking first then it's your own fault.
Finally adaptors won't work to be honest, your offset will be around ET38, the thinnest adaptors are going to be ~18mm meaning that your final offset will be ET20. If you're not lowered that's going to look ridiculous, if you are then you'll most likely need arch work to accommodate the wheels depending on the widths.