Most gearmakers won't cut kevlar due to liability reasons. A kevlar panel is a system of multiple layers, in multiple deniers, in multiple directions, sewn in multiple ways. They are certified as a system, any changes to the system needs to be retested. You may start with a fairly fresh IOTV armor insert but once you cut it down it may not protect the same because it will be missing some of the stitching around the edges.
Buy a pair of serrated or ceramic shears for $25-85 and cut them youself. I'm telling you, its going to suck, you can only cut 2-3 layers at a time, use something to protect your fingers
This is the only pair I have used, made them an offer they accepted. I wound up taping some leather to the finger holes for protection after I got impatient tried to cut 5 layers at a time.
https://rover.ebay.com/rover/1/711-53200-19255-0/1?type=3&campId=5337559805&toolId=10001&customId=j2vl5ue2xd00zk8a00004&mpre=http%3A%2F%2Fwww.ebay.com%2Fitm%2F291713722676:m:mpTCMTRUtihoru1XQ9APqSw