Waveski fin identification help

Hey! I recently acquired a used Wave Master (Aus) Roto 2.5 waveski that is in need of fins (3 fin cluster). The center fin is the classic adjustable longboard style, so no difficulty there. The side fins, however, are fixed, and attach with 2 vertical screws, 1 in front of, and 1 behind the fin blade. I seem to recall that fins of this type were used long ago for side bites on surfboards, before the snap-in fins came into wide use. The base of my fins is approximately 3-1/4" long, 3/8" wide, and the part that fits into the box is ~7/8" deep. The holes are on approximate 4-1/4" centers. I have emailed WaveMaster twice, with no response. Can you help me identify what I have, and tell me if you are (or are aware of) a source for replacement fins? Thank you!