I'm with RAH on the habitat. Give them the habitat and they will be there. They lay a gazillion eggs so just need some cover so the eggs can hatch, tadpoles survive, and some escape predation to repeat the cycle.
Like the pond conditions MSC describes above, if you could dig a small, swampy area connected to your pond (would not need to be very big) that would taper up from six inches deep to nothing and have some type of vegetative cover, I think you will get tadpoles, lots of tadpoles. After I initially cleaned out my old pond but had not yet went around the perimeter making it bigger and the edge deeper, I has such an area flooded at the inlet end (in this case it was just some old fescue grass that had previously been above water level because I raised the pond level a foot more than i originally planned - so had shallow areas I had not planned on). When I would walk or ride by this area, I could see hundreds of tadpoles swim frantically for deeper water.
I cleaned that area out and made it deeper with a backhoe so those frogs may be gone
, but we have a small seasonal creek that transverses between the two ponds and we have boocoo plenty of frogs, so no shortage.
