Tampensis truffles are grown commercially and sold in The Netherlands. Wouldn't be too hard for them to allow the fruiting bodies to grow and obtain a spore print.
It's rare because it was only found and identified once in nature, (i believe) luckily by a mushroom expert who then took the spores and started duplicating the strain from there.
It's rare not only by this, but also by the fact it is harder to find and obtain than the others. Not only are the others more available in nature, but also in thier respective spor-print and syringes.