I can give you a few pointers. In Spain, we have the Portal de Archivos Españoles that is extremely well classified, and in there you can find a whole lot of things.

The Concejo de la Mesta was the guild that managed the wool commerce. Here you have the what there is in PArEs as of now.

http://pares.mcu.es/ParesBusquedas20/catalogo/autoridad/48924?nm

In 1494, the Consulado de Burgos was established as a successor to the Universidad de Mercaderes de Burgos, a medieval guild that managed Burgos' commerce with Flanders. Documents here.

http://pares.mcu.es/ParesBusquedas20/catalogo/autoridad/157418?nm

In Barcelona, in the 13th century, the Consolat del Mar was established as some sort of guild or traders' union. Documents, here.

http://pares.mcu.es/ParesBusquedas20/catalogo/autoridad/46779?nm

Off the top of my head, these are the most easily accessible things I can offer. Of course, the municipal and provincial archives, especially the ones that belong to the Colleges of Notaries are of a lot of help too.

• Lopez, Robert S. & Irving W. Raymond (eds./ trans. ). Medieval Trade in the Mediterranean World: Illustrative Documents. New York: Columbia UP, 2001 (1955): is a collection of the translated primary documents on medieval trade and merchants across the Mediterranean World.
• As for a single primary source text, Francesco Balducci Pegolotti's La Pratica della Mercatura (ca. 1340), written as a textbook for young merchants in the Bardi company in Florence, Italy would be very useful, though most of the text is not translated into English: https://cdn.ymaws.com/www.medievalacademy.org/resource/resmgr/maa_books_online/evans_0024.htm
• Of Pegolotti's La Pratica della Mercatura, at least a part on the travel to China on Silk Road is translated into English: https://archive.org/stream/cathaywaythither03yule#page/134/mode/2up
• Origo, Inis. Merchant of The Merchant of Prato: Daily Life in a Medieval Italian City. Harmondsworth: Penguin, 1992: is a classic example of the utilization of unpublished letters of merchants mostly found in a single archive.

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As for North-Western Europe, neither have we many choices of translated source texts.

• Lund, Niels (ed.). Two Voyagers at the Court of King Alfred: The Ventures of Ohthere and Wulfstan together with the Description of Northern Europe from Old English Orosius. York: William Sessions, 1983: There are in fact several modern editions (and translations) of this indispensable contemporary accounts of the Scandinavian local magnate - merchant - traveler across North Western Europe during Viking Age.
• The Life of Godric of Finchall, the hagiographic literature of the 12th century English hermit who had been a traveling merchant, written by Reginald of Durham is a classical account of the commercial practice in High Medieval North-Western Europe (linked to an translated excerpt)
• Hanserecesse: Die Recesse und andere Akten der Hansetage: is a series of the recorded minutes of the regular congress of Hanseatic cities in Late Medieval Northern Seas. Together with several city chronicles, they are essential primary source texts for the Hanseatic League.
• Among the late medieval and early modern toll registers, Sound Toll Registers online (short: STR online), a record of the Danish Sound Dues, collected from passing ships at Helsingør from the 15th to the 19th centuries are probably the most extensive ones. Notes that this kind of the toll register (called Pfundzoll Buch in German) across European ports, especially in Northern Seas, is often extant in very fragmentary parts. [Added]: Hans Vogtherr (Hg.): Die Lübecker Pfundzollbücher 1492-1496, 4 Bände. Quellen und Darstellungen zur hansischen Geschichte, Neue Folge Band 41, Teil 1 -4; Köln, Weimar, Wien: Böhlau, 1996