It is not known from teh show, as this number or info was nowhere mentioned in the show. Also, it is not known from the books either.
All known Valyrian steel swords are held by great houses, but far be it from that every great house has one. Lannisters didn't have one until they took Lord Starks sword and made two smaller ones from it.
List of known swords in Westeros can be found at Wiki of Ice and Fire.
Also note that there is sword Dawn, that you could see in Tower of Joy event when young Ned Stark fought Ser Arthur Dayne. And later when Ned took it, that is the sword he placed near the Lyanna's bed (with symbol of star on the hilt). It is not Valyrian steel but meteor, or as Westerosi would say "magic stone". It is bright unlike Valyrian steel but is similar in quality. Perhaps we will see more of Dawn in fight against the night.