The official SOULCALIBUR twitter account (@hoshino_calibur) has confirmed today that the PS3 version of both SC5 and SC2HD are currently on sale in the PSN store. They will also be available for streaming play on Playstation Now (at least in Japan) on April 14.
Playstation Now is a cloud based service that allows you to play older Playstation titles on your PS4. With PSNow, you should be able to play various PS3 games on your PS4, with your PS4 peripherals. I can't speak for the quality of this for fighting games, since fighting games are far more sensitive to lag than other genres... but it's been relatively successful for other types of games.