I landed a bottle of this and the gueze two years ago for some Bruery one off stuff if I remember correctly, through an existing trading partner. I then got another bottle of it and the gueze in a trade revolving around a V010 but again that was with an existing trading partner and there was much more involved in the trade. I don't see them offered up much anymore but they are both stellar beers and well worth tracking down. I opened a bottle each at Christmas and was surprised how much fruit is still there and how well the bourbon played into the beer.
I traded for the Geuze about two years ago, forgot what I had to give up but I remember that it took awhile for me to land. These have become even more dear since then so I think it'll take quite a bit to land either of these.
I've had the Geuze and the Golden, but not the Bourbon Kriek. It seems to be the most difficult to land.
I just traded away one of mine for an '09 cuvée de Tomme 750ml and an Upright blend love. I figure when thu release some new R&D sours these are going to be sought after and subsequently hard to land.
If I remember right both were right around 1000 bottles with a 3 bottle limit, released in August 2010. There was a fair amount of trading frenzy around them right away, so I'll wager there aren't too many left in the wild. Mine went to good trading partners almost right away in our standard exchanges of good beer.