Grainger also has stores in Mexico if you are near one they carry lots of electrical stuff . . .
https://www.grainger.com.mx/nuestros-servicios/sucursales
But finding things like the RV specific 30amp plugs in Mexico might be difficult. They have many 30amp outlets but not RV specific - though there are RV parks with outlets that match US RV plugs so they must get them somewhere.
Grainger USA website shows this 50amp outlet - maybe a Mexico store has them.
Receptacle, 50 Amps, 250VAC Voltage, NEMA Configuration: 14-50R, Number of Poles: 3 $9.62 / each Item # 1PKB2 Mfr. Model # 279 UNSPSC # 39121406 Catalog Page # 549 Shipping Weight 0.39 lbs.
Here is the Grainger USA catalog 30amp RV plug - ridiculous price!!
Angle Straight Blade Plug, 30 Amps, 125VAC Voltage, NEMA Configuration: TT-30P, Number of Poles: 2 $43.40 / each Item # 39A771 Mfr. Model # 830-T UNSPSC # 39121402 Catalog Page # 427 Shipping Weight 0.25 lbs.
Pete is probably correct about buying from Amazon if you can't find them in Mexico. You probably have to have a good address. If Pete says it can be done it can probably be done. I found 30amp extension cords with a 30amp plug and an open wire on the other end.
Also 30amp plugs on Amazon
Camco 55283 30 AMP Mini Replacement Male Plug with PowerGrip Handle $13.03
50amp on Amazon
Leviton 279 50 Amp, 125/250 Volt, NEMA 14-50R, 3P, 4W, Flush Mounting Receptacle, Straight Blade, Industrial Grade, Grounding, Side Wired, Steel Strap, Black Price: $5.95