Indeed, Bob, based on what I saw in the pages of Model Railroader magazine back in the day pass exchange was a fairly popular aspect among many hobbyists back around the 1950's and 60's, some even going so far as to advertise in the back pages of MR offering to exchange passes. I believe that Al Kalmbach himself may have instituted the practice given his own printing ability. Pass exchange, of course, followed the century-old lead of real railroads in issuing rider passes to important individuals, particularly those from other railroads. Every once in a while one still sees an original Al Kalmbach pass pop up on eBay, ultimately selling for a high price.
However, the practice apparently has steadily declined with the years in spite of the modern ease and small expense with which such passes can be produced. I believe that, at least until fairly recently, the NMRA had a small Special Interest Group (SIG) membership that still was keeping the practice alive. However, I haven't been an NMRA member in probably about ten years now so I can not accurately speak to that SIG's current status. Personally, I've never participated in the practice. I do note that Googling "model railroad passes" does bring up a number of sites with information and offers to print specialty pass cards. One example is:
http://www.northriverrailway.net/PassTrade2.htm" onclick="window.open(this.href);return false;
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