While this has nothing to do with the Garibaldi Btn or Guadalajara (although the dates are about right), I found another reference to anti-tank rifles in Spain : Abel Paz reproduces in his appendix to "La Colonne de Fer" [Paris : Libertad-cnt-rp, 1997. ISBN 2-9504948-3-8, first published in Catalonia in 1984] the following list of weapons purchased in France in late 1936 or Jan-Feb 1937 at the latest :

Gandia Zone Committee (comarcal) 31 March 1937

CNT-AIT-FAI

List of war material delivered by the zone committee to the confederal column :

500 Lafite bombs, 6000 detonators, 50 periscopes, 3 field range finders (telemetres de campagne), 5 land line telephones (telephones de campagne) 40 field telegraphs (telegraphes de campagne), 40 lanterns 20 batteries for field telegraphs, 2000 bullets of various calibres 1 75mm mortar, 20 rifles of various types, 150 rifles of the "usual" type (fusils courants) 3 machine-guns, 3 light machine-guns (fusil-mitrailleurs), 2 antitank rifles (fusils antichars) 2000 rifle cartridges, 300 grenades

For the zone committee, Bernardo Merino

Of course, I've no idea what ATRs these could be.

Some time ago, a discussion was started with regard to an Anti tank rifle gun present at Guadalajara on with the assault platoon of the Garibaldi btn. Olao Conforti, in his book "Guadalajara: la prima sconfitta del fascismo" identified it as a Solothurn ATR; which seemed a bit strange and left the SCW fans puzzled. Now I'm reading a book by Giovanni Pesce (a Garibaldi btn vet) "Un Garibaldino in Spagna". In the description of the same engagement, on March 10th, 1937, he says: "...the only small anti-tank gun we had is hit [by artillery fire] and destroyed; the commander, Cesare Ravera, is wounded". Cesare Ravera was the commander of the assault platoon . Conforti does not list the book by Pesce among his sources. So, at the very least, the presence of one small AT gun seems confirmed by another independent source; even if its identification as a Solothurn is still unconfirmed.