It will depend upon the type of wastewater you want to make. Plenty of data is available online, follow any relevant literature to replicate the artifical influent. But the most important thing is, preliminary estimation of pollutants (mg COD, TN, NH4-N, TSS, TOC, and metals traces). Better is prepare your own recipe with available chemicals in your lab.
There are many papers in the literature including the use of synthetic water. The researcher need to mention the method of preparing synthetic waste water used in his expetiments.
Synthetic wastewater would be prepared in lab for research purpose but it depends on type of wastewater either domestic or industrial wastewater. Furthermore the variety of industrial waste is also indefinite.
However, you may consider a mixture of desired chemicals (Glucose, Dipotassium phosphate or Monopotassium phosphate, COD, Molasses, yeast), clay, sand, and water/oil. The solution may be a variety of wastewater.
The intensity of wastewater may be controlled by the adding the some chemicals in original wastewater.
The easiest way is to collect the wastewater from the point sources and compare the performance of lab experiment.
I had a similar requirement when I wanted to work with juice industry effluents. After writing e-mails describing the purpose of my study, I was allowed by a nearby juice processing Industry, which gave me a few mL of the sample. After running it through a GC and HPLC, I figured out the components; Later, I formulated my synthetic effluent using the knowledge of the composition.