The gentleman who used to produce Refractol passed away at age 94 about 5 to 6 years ago. He took the formula to his grave even after several people approached him to buy the formula from him. He told me that one of he ingredients in the formula he used to buy from a company in Japan in a 5 gallon container and that company finally decided not to sell it unless he purchased at least 50 gallons. I even offered to help pay for the 50 gallon shipment if he shared the formula with me. But….
Anyway, there have been a couple of products spring up in his wake and I have tried them all. They each do about the same thing that Refractol used to do. But I have to side with Al Balmer in recommending the following web article: https://www.gemsociety.org/article/refractive-index-list-of-common-household-liquids/. This lists several commonly available liquids that you can use. For example, anise oil, cassia oil, cinnamon oil, clove oil and wintergreen oil are the primary examples that have a refractive index close to Refractol (1.567). I purchased samples of all of them and they all work well. The only problem I have with these oils is that they are very pungent and after a short period of time the odor drives me out of the room. I still have them but I keep them in the refrigerator in the garage.
One product that uses wintergreen oil is Refractel. It is sold out of Washington State. Works well and because it has been mixed with another odorless oil the smell is not overpowering.
I have also tried several other concoctions that are available on line but I steer away from them because of their hazardous properties. One of them mentioned in this discussion is the Benzyl Benzoate. After reading the MSDS sheet on this one, I choose to leave the bottle sealed for ever.
Hope this helps.