Hi boubak,
All ot the elements were bought on ebay, here are the links
http://www.ebay.co.uk/itm/5pcs-20x20x15mm-DIY-CPU-IC-Chip-Heat-Sink-Extruded-Cooler-Aluminum-Heatsink-New-/322519635950?hash=item4b17ab17ee
This one needs to be modified by cutting off one row of pins
You would also need thermal adhesive like the one below as only the smallest radiators comes with it
http://www.ebay.co.uk/itm/3M-Thermally-Conductive-Adhesive-Tape-1-x-1-25mm-x-25mm-2pcs-/182325577276?hash=item2a7373863c
This is the thermal silicon pad I’ve used but it’s quite thick (2mm) so probably something thinner like 1.5 or even 1mm would do the job even better it probably depends on the hight of the biggest parts on the back of LimeSDR so you have to measure this.
I hope this helps, good luck cooling down your SDR 