Hi,
AFAIK OpenSDA does not support S32R274. Anyway to be 100% sure please check it with Pemicro support (OpenSDA release notes are not very specific about supported derivatives)
Regarding OpenSDA bootloader/application - Pemicro distributes it in a single package along with other OpenSDA firmwares:
http://www.pemicro.com/opensda/
The bootloader/application is distributed as .sda file and could be programmed e.g. by CycloneMAX programmer.
For more information about OpenSDA I'd suggest you to contact Pemicro Support.
Hope it helps.
Stan