Where do I find the secrete vin code on A 1969 dodge superbee?

There is no "secret" VIN number on the Superbee, you will find one on the left side of the dash visible through the windshield, one on the underside of the radiator crossmember (I think it's on the underside), one on the cowl, and if equipped with the original engine and transmission it will be found on them as well. Also if you can find a "build sheet" which can be attached to the underside or rear of the glove box insert, under the springs on the rear seat or rear seat back or sometimes under the carpet if carpeted and has been known to be found even under the trunk mat, that too will have the VIN number.