To clone miRNA you will need two linkers, one 5' and one 3'. IDT offers the 3' miRNA linker, however we currently do not offer a 5' linker. You may want to consult the original Lau article for miRNA construction and see their 5' linker design as a reference.
Lau NC, et. al. (2001) An abundant class of tiny RNAs with probable regulatory roles in Caenorhabditis elegans. Science. 294:858-62.