Varkonyi-Gasic and Hellens, (2011). This article gives you an idea to design primers for miRNA. I used the same strategy for the screening of virus as well as plant miRNAs. It worked.
Varkonyi-Gasic, E., Wu, R., Wood, M., Walton, E. F., & Hellens, R. P. (2007). Protocol: a highly sensitive RT-PCR method for detection and quantification of microRNAs. Plant methods, 3(1), 12.
If you are looking for miRNA primer, then prefer pre-made primer from company. miRNA primer have universal primer sequence, upon which company synthesize with little chemical modification to for stability and to enhance specificity.
Rest gene primer can be synthesized using primerblast..