The Gladesville Guitar Factory has one of the broadest ranges of classical guitars in Sydney.
The Classical Guitar Society runs an annual Sydney Guitar Summer School in January over the Summer Holidays. There are lectures and performances from visiting artists. The Summer School usually runs over 5 days and culminates in a performance of several ensembles.
The Sydney Eisteddfod has a Classical Guitar category providing an opportunity for performance in a competitive environment. There are three age categories.
The Adelaide Guitar Festival is a great event to attend if you have can make it. Its current artistic director is Slava Grigoryan. The Festival has developed a following which attracts international artists and is associated with the more established Cordoba Guitar Festival. You may find these visiting artists performing is Concerts in Sydney on their way to or from the festival, so look out for them around the time of the festival.
For overseas opportunities, the Cordoba Guitar Festival is an annual event in Cordoba, Spain. It's well worth a visit if you find yourself in Spain around July. It attracts international players from diverse Genres ranging from Classical, Flamenco through to Jazz and Rock.