How many galaxies have had their distance determined using SNIa?

Supernovae of type Ia can be used as standard candles to determine extra-galactic distances. But these event only occur (roughly) once every 200 years in any given galaxy and rapidly fade away. So to actually see a supernova in another galaxy, you have to be observing a lot of galaxies for a long time. This makes it seem like this isn't a very practical method to determine extra-galactic distances. To how many galaxies has the distance been determined using type Ia supernovae?

• "standard candle" is the keyword :-) Note, in the last 50 years, we could have seen supernova in 25% of the galaxies. – peterh - Reinstate Monica Jan 22 at 14:52
• ...of the galaxies that we have been looking at non stop. – usernumber Jan 22 at 14:53
• Enough if we make a single photo about it in the $\approx$ 1 month until the SN is visible. – peterh - Reinstate Monica Jan 22 at 14:55
• This paper mentions using 740 spectroscopically conﬁrmed type Ia supernovae with high quality light curves arxiv.org/abs/1401.4064 – D. Halsey Jan 23 at 0:46
• No, it isn't a good way of determing distances if your aim is to determine the distance to every galaxy. But thast isn't what they are used for. – Rob Jeffries Jan 29 at 11:06