There is some information here: http://www.feldgrau.net/forum/viewtopic.php?f=55&t=3125
If memory serves me correctly Italy recruited Slovenes from Venezia Julia into its army just like any other Italian citizens. I believe that the British took in over 4,000 Slovene deserters or prisoners from the Italian Army in North Africa, 300 of whom already formed the nucleus of 1st Yugoslav Royal Guard Battalion by August 1941.
According to my information only 35 Yugoslav officers and 20 Yugoslav other ranks had succeeded in escaping to British lines in the Middle East by late 1943. If so, it is still probable that the Yugoslav Royal Guard Battalion was initially largely formed from ex-Italian Slovenes. There were about 100,000 Italian prisoners in British hands by August 1941, so it is not too unlikely that there were 300 Slovenes amongst them.
It was not until the Operation "Compass", when two prominent Slovene politicians who were politically active in Egypt even before the war, pressed on the Royal Yugoslav Government to allow Slovene POWs from the nearby Al-Agamy Camp to enlist themselves into the 1st Royal Yugoslav Guards Battalion, which was at that time badly understrength with only about 100 men, most of them army officers. Soon new recruits were pouring into the battalion, including those from Italian East Africa, Somalia, India, Kenya, South Africa, Palestine and some even from Argentina and the French Foreign Legion in French North Africa. When enlisting into the battalion, each recruit swore to the King Petar II. and received a Yugoslav citizenship, thuis revoking the Italian one, so that by September 1943 all soldiers were technically Yugoslav citizens.
In mid-June 1942 the Royal Yugoslav Guards Battalion was formed in Agami Camp next to the barracks of the Czechoslovaks. At the beginning of August 1942 came into the battalion more than 100 Slovenes who had returned from Tobruk, where they have served with the Polish Brigade. At about that time the battalion's strength was arounf 300 men. Alone on 2 January 1942 some 150 new Slovene POWs came, raising the strength of the battalion up to 500. The battalion saw very little action. As a part of the 10th Brigade of the 5th Indian Infanty Division they were sent to the oasis Kennels Box in the Libyan Desert, later to Halfaya Pass, never encounbtering any enemy afterwards they were pulled back to Trandjordan.
According to my source, around fifty specially selected men from the Royal Yugoslav Guards Battalion in Palestine and Jordania were sent to Eastbourne, England, in early 1943 to complete command traning and to form a special troops inside the 10th (Inter-Allied) Commando.
After September 1943, when the story about Tito fighting against the Germans and Mihailovic not, majority of the men of the Royal Yugoslav Guards Battalion, Royal Yugoslav Navy Squadron and various supply units joined to some of the Tito's forces which were at that time headquartered in Southern Italy. Only a small contigent of men remained loyal to the Royal Government, probably less than a company and several warships in Taranto. They were mostly drafted into the American or British armed forces in Southern Italy and saw some combat in Southern and Northern Italy in 1943-1945. However, they should not be mistaken for "Yugoslav" labour companies in Sardinia, Corsica and Southern France in 1943-1945.