I don't know if it is possible to buy aftermarket mirrors but a lot of kits will have two sets of mirrors,usually the normal ones and the chromed ones...After building a couple of kits,you will be left with spare wheels,mirrors,engine pieces and a lot of other usefull pieces for your later on builds. I keep everything that could be usefull to me including old electronics,old tools or metal pieces,everything! (Im getting crazy on this though) .
BTW. Very nice Gremlin,i love the color!