Byzantine vambraces
A thorough discussion of the topic (with detail of relevant finds and depictions) can be found thanks to an article by Peter Beatson the New Varangian Guard .
There is some limited evidence that some tenth and eleventh century Byzantine regular soldiers wore vambraces on their forearms (and, for cavalry, also upper arms and lower legs), made from a series of metal plates running along the arm, sewn or riveted onto a cloth or leather backing. These seem to have been restricted to better-equipped heavy cavalry, modelled on the heavily-armoured elite cavalry of the steppes, ultimately going back to Hunnic and Avar models of the fifth and sixth centuries. We would not expect them to have found their way into use elsewhere in any numbers.
Earlier Byzantine military manuals (notably the early seventh-century Strategikon by Maurikos) mention armguards (manikellia or cheiropsella) and greaves (podopsella or chalkotouba) made of iron or wood. The Tactica of Emperor Leo VI (c.900) drew heavily on such texts, and describes both heavy cavalry (kataphraktoi) and heavy infantry (skutatoi) wearing arm-guards. Leo clarifies the cavalry armguards as cheiromanika sidera ('iron armguards'), possibly indicating that the infantry version used wood.
Varangians and vambraces
Whether foreigners in Byzantine service (in particular the Varangian guard) were ever equipped with splinted armour is debatable. It is certainly not impossible, but there is no evidence for it. Rather, the concept seems to have appeared in an early re-enactor publication, been picked up in an Osprey volume of 1980 and become part of the canon of 'received wisdom'.
Even if members of the Varangian guard did wear splinted limb armour, there is no reason to suppose that it would find its way to Scandinavia in any quantity. The Byzantine army was supported by a large and relatively efficient bureaucracy, and it is highly unlikely that any self-respecting quartermaster would allow significant quantities of military kit to leave in the hands of barbarian foreigners.
Byzantine vambraces in the Vikings Society
Please note that 'splinted' vambraces of this type may only be used as part of a full Byzantine kit, i.e. at an event where the Society is portraying Byzantine regulars. Such vambraces may not otherwise be used.
Credits: this draws heavily on an excellent article by Peter Beatson for the New Varangian Guard .