How many devices can you wear on a ribbon on the Army Service Uniform?

AR 670-1, 29-12 states . Wear of appurtenances
Appurtenances are devices affixed to service or suspension ribbons, or worn in lieu of medals or ribbons. They are worn to denote an additional award, participation in a specific event, or some other distinguishing characteristic of an award. The following appurtenances are authorized for wear on decorations, medals, ribbons and other awards, when authorized by appropriate authority. When more than one appurtenance is worn, soldiers will ensure all devices are centered on the ribbon. (See AR 600–8–22 for additional information.)
a. Oak leaf clusters.
(1) A bronze twig of four oak leaves with three acorns on each stem is worn to denote award of second and succeeding awards of decorations (other than the Air Medal), the Army Reserve Components Achievement Medal, and unit awards. A silver oak leaf cluster is worn in lieu of five bronze oak leaf clusters. It is worn to the wearer’s right of a bronze oak leaf cluster and to the left of the “V” device. Oak leaf clusters, 5/16 inch in length, are worn on service ribbons, the suspension ribbon of miniature medals, and unit awards. Oak leaf clusters, 13/32 inch in length, are worn on the suspension ribbon of full-size medals. Oak leaf clusters 5/16 inch in length, joined together in series of two, three, and four clusters, are authorized for optional purchase and wear on service ribbons and unit award emblems. Personnel wear oak leaf clusters centered on the service ribbon and suspension ribbon, with the stems of the leaves pointing to the wearer’s right. If four oak leaf clusters are worn on the suspension ribbon on either full-size or miniature medals, the fourth one is placed above the middle one in the row of three. No more than four oak leaf clusters can be worn side-by-side on service ribbons.
(2) If the number of authorized oak leaf clusters exceeds four and will not fit on a single ribbon, a second ribbon is authorized for wear. When the second ribbon is worn, it is placed after the first ribbon; the second ribbon counts as one award. Personnel may wear no more than four oak leaf clusters on each ribbon. If the receipt of future awards reduces the number of oak leaf clusters sufficiently (that is, a silver oak leaf for five awards), personnel will remove the second ribbon and place the appropriate number of devices on a single ribbon.
b. “V” device. The “V” device is a bronze block letter, “V,” 1⁄4 inch high. It is worn to denote participation in acts of heroism involving conflict with an armed enemy. The “V” device is worn centered on the suspension ribbon and service ribbon on the Air Medal, Bronze Star Medal, Army Commendation Medal, and the Joint Service Commenda- tion Medal. Not more than one “V” device is worn on a ribbon. When worn with an oak leaf cluster or numerals, the “V” device is worn on the wearer’s right.

Hopes this answers your question. Ribbon plus 4 Bronze OLCs equal 5 awards. One Silver OLC equals 5 awards, OLC's are worn to the left of V device. 6 Awards and V looking at ribbon infant of you, V Silver OLC Bronze OLC. Remember, the ribbon itself is one award.

Have you looked in AR 670-1 or perhaps AR 600-8-22?

Well, if you've looked and haven't found the answer I will tell you what I would understand to be the case. At most 4 OLCs, with 4x silver OLCs representing the most you can with one ribbon. If you need to show more, you need another ribbon and you show your additional appurtenances on that one (keep in mind the ribbon itself counts as an award and the V device does not).

So, to tie into your example, say I have 6 ARCOMS, one with V device. I would show that as an ARCOM ribbon with 4 bronze OLCs (accounting for 5 ARCOMS) and another ribbon with the V device (accounting for the 6th ARCOM and the Valor designation.

Whatever fits on one ribbon goes, from your centerline towards your shoulder... V device, silver OLCs, bronze OLCs.