Manual work as source of entropy
Just gather every source of randomness you have all together and apply a 256-bit secure hashing function to it such as SHA-256. The advantage of this approach is that it is as secure as its strongest input up to the limit of the hashing function you use.
There is no benefit to discarding information. Why map 3 and 5 both to 1 and give up some entropy? What benefit would you get?