I'm trying to find the 4"x8" velcro panel that attaches to the Molle on the front of my carrier, that I can use to secure a Haley chest rig to. I have it clipped on but would like it a little more secure

Off the top of my head there's a few things that might fit the bill for your needs.  

Vertx makes some die cut velcro that weaves thru molle.  I've never used it but it seems like it would work and be lite weight and low profile.  With a little ingenuity, strips of velcro one wrap could easily be weaved thru as well as long as they're not the main attachment point and the Haley rig buckles do the heavy lifting.  

Old school patch panels can be found too but I would think they'd add unnecessary bulk.  If you go this route, don't get a huge one, just bug enough to keep the Haley rig from shifting around.



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There is plenty of 4" wide velcro on eBay.  This seller has it by the foot.

Here

For his purpose, I think one wrap would handle it just fine.

Hit up Redwire Gear, redwiregear.com,  here in PHX. I know they do some custom work.