Bacta was invented by the Vratix on the planet Thyferra in antiquity, with the galaxy at large learning of its properties around 4,100 BBY (src: The Essential Atlas). So by the time of ABY it became fairly widely used, though not 100% ubiquitous due to supply constraint.

Bacta was used for a while, but for a time shared the market with Kolto.

When Kolto supplies collapsed, Bacta became fully widely used.

Bacta was synthetic, but mostly produced on 1 planet.

Bacta was invented by the Vratix on the planet Thyferra in antiquity, with the galaxy at large learning of its properties around 4,100 BBY (src: The Essential Atlas). So by the time of ABY it became fairly widely used, though not 100% ubiquitous due to supply constraint.

Bacta was used for a while, but for a time shared the market with Kolto.

When Kolto supplies collapsed, Bacta became fully widely used.

Bacta was synthetic, but mostly produced on 1 planet, until the events of X-Wing novel "The Bacta War", when the Vratix finally exported the process off-planet.