I can appreciate your desire to customize something that you own, however, barrel shrouds are a point of contention for the antis. They've been named on many occasions as an "evil" feature that turn our sport rifles into baby and nun killing objects of destruction.
If the rifle sees frequent range use, I'd suggest that you forgo the barrel shroud, as it serves no real purpose on a Mini 14. We have an up hill struggle before us and if we want to keep our sports utility rifles, we need to do all that we can to keep them from looking "evil" to those that seek to strip us of them.
Just my 2 cents.
If your heart is set on one, you can find them, in stock, here: Mini-14/M14 Accessories