Have any of your vets considered GME? We have had several very young Maltese on another forum I belong to have dogs diagnosed with the disease. It is very difficult to diagnose and unfortunately very expensive. I know it requires an MRI and spinal tap. The prognosis isn't very good, either.
http://www.marvistavet.com/html/body...encephali.html
My Lady has idiopathic epilepsy which is true, organic epilepsy with no known cause. It's unusual in a dog under a year old as seizures are usually caused by an underlying condition like a liver shunt, thyroid irregularities, etc. This is a fabulous website loaded with information:
http://www.canine-epilepsy-guardian-angels.com/
My heart goes out to you. You are in such a difficult situation. Vet bills can run into the thousands quickly with no diagnosis. Did you get a health guarentee? Is your breeder helping you at all with the vet bills?