I would like to grow strawberries, blueberries, camellia(Camellia sinensis) and a couple goumi(Elaeagnus multiflora) bushes in the same garden bed. They are all acid-loving plants, luckily.

Could anyone tell me what peat:compost ratio I would need to get to a pH of 5.5 for a raised bed? This would be assuming a compost pH of about 7(Black Kow composted manure and Black Velvet mushroom compost).

I use SFG for my annuals, and that pH is ~6.5. It's 1/3 peat moss(pH of 3). But since pH is a logarithmic scale, I'm unsure of the actual formula to lower it further.

I don't know anything about using peat moss, sustainable sources or not: (I've seen the PRI thread), but your general soil is around ph 6.5, right?
In my experience all the plants you mention except blueberries will grow ok in that ph.
My ph is 6.8 and blueberries would be miserable here!

Yes, it is mostly for the blueberries. I've tried sulfur and pine bark/needles, but my "soil" seems to leach everything too quickly. I guess it's off to experiment for myself.

In my experience, blueberries forgive a slightly less than perfect ph, if you give them lots of yummy organic matter. On a side note, I mulch mine with pine needles.