Combining two hashing functions
For the purposes of a bloom filter you need a number of hash functions. Cryptographic hash functions are designed so that changing a single bit in the input should change many (around 1/2) of the output bits.

So, say you have a good hash function $h$ (e.g., SHA256 though MD5 should work for your purposes too) a good option for you would be to use use:

$h_1(m)=h("1" || m)$
$h_2(m)=h("2" || m)$
$\vdots$
$h_n(m)=h("n" || m)$  

Where $||$ is concatenation. Then you only need one hash function. This is basically what they are doing in this java implementation.


  Is there any existing literature that describes the loss of distribution?


Not that I am aware of. But think about it this way, if there were a significant change from the uniform distribution computable in a reasonable amount of time we wouldn't use the hash function for cryptographic purposes.

Now, is there some sort of attack you are worried about?