Bach wrote one of the cello sonatas for 5 string cello. There are some baroque 5 strings about that would suit. Emily and I looked into making one for TwoTree about 3 years ago, but the price to ship it was prohibitive at the time, and we didn't follow through.
It seems that the 5-string 'celli like the one Bach wrote for have a high E string, and may even lean towards being a bit on the small side. The one pictured on the Ithaca String website is a 3/4 cello, so my assumption is that it would have the extra high string. Maybe my best option is to buy a big cello and have it converted.
Andrew, I don't make cellos but I think the conversion idea is a pretty good one if you can't find anybody that makes a 5 string cello. I would certainly love to hear the music made with a 5 string!!
Yes - I think you're right. A conversion might be the right idea. I suppose one thing to watch out for would be the difference in tension on the top of the instrument and the neck. I know that converting a double bass to a five string is not something that is easily done for this reason. The bass bar has to be strengthened, and I'm sure there are other considerations as well.
On the topic, maybe a good approach would be to get a cello 'in the white' without holes drilled for the pegs or fingerboard or bridge or tailpiece from a manufacturer somewhere (maybe in China?) and finish the instrument here in Canada with a good luthier. Any suggestions as to where I might look for something like that (the cello I mean, not the luthier - I know a few of those...)?
I did a Google search for white cello and found some. You may have to plug some of the tuner holes and re-drill for your pegs. Most "white" instruments already have the peg holes drilled.
A "church bass" or "Yankee bass" most commonly made around 1700 - 1800 in the New England area, could be converted to a fine 5 string bass with a low F. You would need to find one that is ideally a little bigger than a cello, and a lot of them were. I have come across a couple that would fit the bill. I think I know where one is that could be converted. Do a little google search and see what I am talking about. Some were actually made with 5 strings, and a lot of them had gears instead of pegs. They all have character and did not really follow a classical pattern but are simetimes quirky. But they were usually made with good yankee craftsmanship and some were converted to cellos and sound beautiful.
They are not too expensive considering their age, so it might be the best way to go for a nice old instrument. I think you could find one for around $2000 to 3000 and have it converted for whatever your luthier would charge. I would love to do the job, it would be interesting.