Been looking myself. Found the longer/bigger ones on Amazon that Bitmine used in that pic of one of their boards where the long bottom sink fell off. Biggest problem is coming up with a clip of some sort to make sure they say put. Either that or use thermal glue to make it permanent.

If to be kept repairable I'm thinking more of a thick riser bar spanning several chips and milled for clearance that can be bolted down to give a nice wide surface for bigger sinks.

Considering there should be no need to replace the chips, I think gluing on a bigger sink milled if needed (or use a spacer) to clear caps would be best overall. I'm using http://www.amazon.com/Arctic-Alumina-Thermal-Adhesive-Tube/dp/B0009IQ1BU with 1/4" aluminum cubes on my Ants to link the Vcore switchers to the big heat sinks. Should only need the tiniest dollop but only 5-min work time so don't mix more than ya can use.

edit: Hmm. These folks look interesting for sinks http://www.alphanovatech.com/?gclid=CLzm7snhyr4CFckWMgodGjIA3A The 1/8th brick (a telecom size) power converter series looks very promising indeed..http://www.micforg.co.jp/en/cat_dcce.html#eighth-brick