D-ribose supplementation helping CFS/FM is likely because natural production by the body is reduced. “By the body” often means by the microbiome. For example a body that produces not enough B-12, is because it is low in L. Reuteri that makes the B12.
So what bacteria makes D-Ribose? What I have been able to find via PubMed are:
- Bacillus subtilis   
- This family include Natto (from which Nattokinease is derived), an acquired taste Japanese dessert.
- Bacillus pumilus 
See also these posts
“Cultures of B. subtilis were popular worldwide before the introduction of antibiotics as an immunostimulatory agent to aid treatment of gastrointestinal and urinary tract diseases” [wikipedia]
- “We examined two commercial B. subtilis probiotic preparations, Enterogermina and Biosubtyl. Surprisingly, physiological and genetic characterization of the bacteria contained in each of these preparations has shown that neither contains B. subtilis….. instead Bacillus species that are closely (Biosubtyl) and distantly (Enterogermina) related to B. subtilis. ” 
- “Bacillus subtilis is used to produce many antibiotics, such as difficidin, oxydifficidin, bacilli, bacillomyin B, and Bacitracin,…Bacillus subtilis is also used as a fungicide” [Probiotic.org]
While there are studies of d-ribose and CFS (positive results), there are none for bacillus subtilis. I could not find a single strain/species probiotics (excluding those cited above). The production amount of ribose is strain specific. What does contain some are:
- Prescript Assist – effective for IBS
- Threelac Probiotic on Amazon (60 packages for $42) – bacillus coagulans, bacillus subtilis and enterococcus faecalis – no studies on PubMed
- Update: Unpasturized doenjang (Korean f0od), available on Amazon.
- Natto, a Japanese dessert food! – I do eat this, originally as a source of nattokinease, but now I have a second reason for eating it!!
Last, it should be mention that it is also called hay bacillus or grass bacillus because that is where it is very often found. A hundred years ago, when most of the population lived on farms, people would have gotten a rich supply of this. In today’s world, there is a greatly reduced exposure to hay or grass (and thus the bacteria).