how to make hibiscus bloom

A good source of potash might help--kelp meal, K-Mag, Jersey greensand, chopped, dried banana peels, etc.
Also make sure that it is getting enough sun. Most varieties need at least 4 hours of direct sun each day.

Bone meal has phosphate and nitrogen so best not to use. Epsom salts contain magnesium which won't do the trick. If your 'bloom fertiliser' (potassium) hasn't worked then I would recommend not feeding anything and starve the plant. Lack of any fertiliser will put the plant under stress and could force it into bloom.

Unless you live in 'Death Valley,' rarely will you ever need to supplement the soil with magnesium, potassium or nitrogen. These are all naturally occurring elements that are generally replenished naturally as bio matter decomposes. Rainwater is loaded nitrogen.

Did you know that a bolt of lightening will fertilize the soil? I'm going to print this because it's fascinating.

...'in a thunderstorm there is enough electrical energy in lightning to separate the nitrogen atoms in the air. Once the atoms are separated they can fall to earth with rain water, and combine with minerals in the soil to form nitrates, a type of fertilizer.

The nitrogen-containing nitrates in the soil are absorbed by the plants, and when we eat the plants or the animals which eat the plants, we get the nitrogen in a form which our bodies can use.

http://indianapublicmedia.org/amomentofscience/lightening-helps-fertilize-soil/

How do I make my hibiscus bloom? I don't do anything. I just leave them alone and they bloom on their own because that's what they do. It's a royal pain pulling up all the saplings growing up everywhere. Just give it a sunny place & that's it. Trim it to size when necessary -otherwise I don't ever think about them. God takes care of them for me.

Bathgate, Jerry says that he is gardening in Florida. There, most of the soils are developed from ancient coral reefs, and are likely to be poor in all kinds of mineral nutrients.
Jimmy, many brands of bone meal sold here in the States are steamed, to salvage the gelatin, and so have little or no nitrogen. Also, "bloom food" marketed here in the States are mostly phosphate, which doesn't help Hibiscus to bloom, unless it is in extreme deficiency. Other than that, starving it--in moderation--may be the way to go.
Jerry, there is another possibility that I just thought of. If the bush is developing flower buds, but they are turning yellow and dropping off before they bloom, the problem may be overwatering. If you are giving supplemental watering, you might want to do so less often. Hibiscus are more drought tolerant than most people think. Also, if you are shearing the bush frequently, you may be cutting off most of the buds before they bloom.