I can understand your concern,but there is no such thing existing as it is not possible to preserve the kidney
beyond a certain point.
Secondly the answer lies with you as the best donors are the close relatives of the patient.
THere are other options like exchange/swap donation, cadaver donation,so do not get disheartened & make all out efforts for the options mentioned.
Lastly a word of strong caution for you to not fall in a trap to get a kidney on sale or other such advertisements.
Best Of Luck