Why bother? The standard bumpers suit the car rather well. You could always experiment with removing the over-riders for a cleaner look, or colour-coding the chrome bumper blade if it's badly pitted.
For wider wheels, the usual and easiest choice is the LP917 van rims which are an inch wider than standard at 4.5J and will take a 165-width tyre. Then, there are the even rarer LP936 'reverse rim' van wheels, which look great but are as rare as Hen's teeth to find, and would still only take a 165-width tyre.
Other than that, if keeping the standard 4" hubs PCD and 14" diameter, you are limited to Jensen-Healey alloys, Minilites or Weller's new range of wider steel wheels, unless that is, you can get a set of wheels banded to suit.
You can alternatively fit MG Midget/Austin Healey Sprite wheels, but they are 13" diameter and look a bit too small on the Minor.