I had the same problem.
Best thing to do is to contact THM themselves and ask them to send a couple out to you. It was free for me. They even sent me crank arm stickers to replace my scratched ones when i told them i'm planning to repaint the cranks.
They're fantastic with after sales service. My cranks wasn't bought new and they didn't care.
You'll find it hard to match the bolts from any other place. You'll notice the head of the bolts are round. It's pretty hard to find round ones. I tried to get some from ebay and the head was tight inside the recess part of the hole. I could never be sure the torque setting was clamping pressure or it was getting stuck in the bolt head recess in the arm. Also, standard bolts have a taller head so they stick out of the arm a bit more.