Travel Insurance UK to Europe

Hi everyone! My dad had an LVAD implanted in May 2015 and has since being doing really well. We have booked a family holiday away to Turkey this August however having trouble to get my dad insured for his LVAD and Dilated Cardiomyapathy- has anyone got any suggestions? Or what travel insurance companies has everyone else used???? The hospital want in writing that the LVAD is covered under the insurance- help??!!