I think the answers are in the Parts Catalog.
Click Manuals at the page top, then "I agree" and then select the UK Spec EA11R Catalog (Your car is the JDM one, so the Catalog below it is really the one for it, but there is no difference in this area, so you might as well use the one in English
).
Go to Fig 68, and you'll see the shapes you need (parts 5 and 6). They are secured with 12 nuts and 12 washers (parts 10 and 13). I guess the bolts are captive to the bumper.
If the bolts aren't there, perhaps you could drill some pilot holes and use self-tapping screws and washers. If they are too rusted to use, perhaps you could substitute small cable ties for the nuts.