Are your sure that your were talking to S&W and not some gunshop? I ask because the barrel has NOTHING to do with ignition, it's the part that the bullet passes through on the way to the target.
Now, if you are referring to the CYLINDER there is a remote possibility of it effecting ignition. However, it is highly unlikely and I would expect that S&W still has a stock of cylinders for the model 66 in their warehouse, generally S&W warehouses parts like this for 10 or 15 years before they sell them off.
In addition, there is the matter of the no questions asked lifetime warranty. If S&W cannot repair your revolver due to a lack of parts or non repairable damage to the frame they will replace it with a new similar model. Since the model 66 has been dropped from production that means that they would most likely offer to replace it with a new 686.
Seriously, whoever told you that you need to find a new barrel is either a complete idiot or you weren't talking to S&W. I would suggest that you take a look at your paperwork and confirm where you sent that revolver.
Finally, I'll note that IMO 90% of the complaints about misfires are resolved by simply removing the grips and tightening the strain screw on the bottom front of the grip frame. If they are not properly tightened the strain screw WILL shoot loose over time and when it does the result is misfires. Basically, had you asked for some guidance on the forum you could have probably fixed your problem in about 3 minutes.
