I think that colour temperature and length may have been made for lighting aquariums at one point. They had some pretty oddball colour temps for aquariums at one point. It'll be a F15T8 lamp though but almost all F15T12 fixtures will run the F15T8 lamps.
In terms of general lighting lamps, Sylvania made F32T8s in 8000K. Menards has them.
That might be a possibility to find a 15W Lamp. However then the quality will certainly be not very good or the lamp very expensive. Osram Augsburg and Smolensk did made 8000K tube, however only in 18, 30, 36 and 58W if I remember correctly. Another possibility would be to use a 6700K with high CRI, the light from these is also very nice.