The available evidence strongly suggests that the Franco-Scottish army at Bauge was primarily made up of Scots, probably in the region of 4,000 to 5,000 with perhaps slightly more than 1,000 French.
The Chronicles of Enguerrand de Monstrelet give only numbers for casualties, while the chronicles of Jean Le Fevre and Jean de Wavrin state only that the English were outnumbered two-to-one by the 'daulphinois' (i.e. Scots and French). However, the composition of the Franco-Scottish army can be tentatively deduced from the fact that Scots were the mainstay of the anti-English forces at the time.
A Scottish army of around 6,000 sent to France in 1419 under the Earls of Buchan and Wigton. These were split up, with some being used in garrisons while the bulk were in the field. Further recruits arrived the following year; how many exactly is unknown, but they were fewer in number than the original force. The only other forces available to the French Dauphin (the future Charles VII) at the time were those of Gilbert Motier de La Fayette, who had only around 1,000 men, and an unknown but small number of recent local recruits. The French Dauphin's recruitment efforts were hampered by a lack of funds, which accounts for the Scots being the mainstay of his forces at the time.
As for the battle itself, two noted academics for the period have come up with roughly the same estimates:
Buchan’s Scots were accompanied by a smaller French force commanded by
Gilbert de Lafayette, a well-known figure who had already made a name
for himself as the defender of Falaise and Lyon. They were joined on
their way by fresh recruits raised locally in Anjou and Maine
including the celebrated routier captain La Hire. In all, there must
have been between 4,000 and 5,000 Scots and about 1,000 French troops.
Source: Jonathan Sumption, 'The Hundred Years War, vol IV: Cursed Kings' (2015)
Juliet Barker, in Conquest: The English Kingdom in France, 1417-1450, also gives a figure of 4,000 Scots:
On 22 March 1421 his [English King Henry V] brother and heir,
Clarence, to whom he had given supreme military command in France
during his absence, had unexpectedly intercepted a newly arrived
contingent of four thousand Scots at Baugé in Anjou.
Evidence relating to the aftermath of the battle further suggests that the Scots formed the large majority of the Dauphin's army at Bauge; it was the Scottish commanders who were rewarded by the Dauphin and the Scots held most of the English prisoners, profiting greatly from ransoms paid by the English:
If the Scottish chronicles are to be believed, the French tried to
steal the glory of victory from the Scots and were only found out when
it became clear that the latter had the majority of the prisoners;
Charles is reputed to have scolded his nobles for having described the
Scots as "Mangeurs de moutons et sacs de vin" in the past. Certainly
the profits flowed to the Scottish leaders.
Source: B. G. H. Ditcham, 'The employment of foreign mercenary troops in the French royal armies 1415-1470' (PhD thesis, 1978)
Note that it's hard to pin down precise numbers for most battles during the Hundred Years War; even the size of the armies of more famous ones such as Agincourt and Crecy are much disputed. Chroniclers often disagreed on numbers, if they stated them at all.