When there is a well-attended event, it can get tight, but street parking can be found withing 2 or 3 blocks.
For evening events at SPC, I often find parking across the street along 6th. Parking within several blocks is metered on weekdays and Saturday until 6pm.
There is also a lot in Balboa Park across 6th Avenue that often has space. The entrance is a little hard to find; it is to the north on 6th a few blocks.
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