Here's one made by Hella. It was standard fare in all IMSA prototypes in the 80's and 90's when I was building them. Summit Racing has them for around $18 (plus $8 for shipping). I have a brand new one I'll sell you cheap if you're interested. PM me.
Summit Racing Battery DisconnectsThe Hella battery disconnect is in the middle at the bottom of this link.
Don't let its price fool you; It's a well made switch. Once you remove the key, the switch acts like an anti-theft because without it (the key), you can't re-energize the car's electrical system.