I'm afraid if you're planning to invest zinc explorers, developers, and miners, you will need to find a broker who handles Canadian- and preferably also Australian-listed stocks, either directly or through pink sheets.
I will post my entire watch list of zinc companies, formatted for two Yahoo portfolios, and you shouldn't have too much trouble picking out the US-listed ones. Some of the others may also have dual listings, but as a Canadian I don't have to pay attention to that. V & TO are canadian, AX is Australian, HK is Hong Kong, and L is London.
Two provisos:
1) do not mistake inclusion in the list for endorsement;
2) most of these companies also mine or are looking for other metals as well.
0166.HK ABI.V ABR-P.V ABU.AX ADA.TO ADD.V ADK.V AEM.TO AET.AX AGU.L AHD.TO AIM.AX AMC.TO AOX.V APE.V APG.TO AQA.TO ARE.AX ASX.V ATX.V AULO.OB AVI.AX AXR.TO AYM.L AZS.AX BAJ.TO BBR.V BEL.V BFD.V BLS.TO BMK.V BN.TO BSM.AX BTC.V BWR.TO CAA.V CBH.AX CCM.TO CEM.V CGG.AX CGMX.PK CLZ.V CME.V CON.L CPP.V CRL.AX CS.TO CSE.AX CXB.V CYP.V CZN.TO CZX.V DEG.AX DIB.V DJI.V DMM.AX DON.V DRA.V DRK.AX EGU.TO ELN.V ELO.V EMED.L EML.L EOX.V EPL.V EVR.V EXS.V FAN.TO FMM.V FMNJ.PK FNT.AX FNX.TO FOR.TO FPX.V FV.V FXR.AX GAI.V GBS.TO GCR.V GFM.L GMX.TO GQC.V GXP.TO HBM.TO HER.AX HER.L HLO.V HRG.TO IBC.AX IMN.TO INL.AX IZN.V JML.AX JNY.V KAH.L KAR.V KCR.TO KEX.V KZL.AX
LAT.V LEG.AX LRL.L LTH.V LTR.AX LUN.TO LYD.TO MAM.V MCR.AX MD.V MDV.V MGR.V MIO.L MLS.AX MMB.AX MMG MMI.V MMM.TO MMN.AX MMS.L MNR.TO MOA.V MOX.AX MTB.AX MTX.V MXI.V NL.V NMI.AX NOT.V NST.AX NUS.TO NW.V OVR.AX OZL.AX PDZ.AX PEB.V PEM.AX PGR.V PMM.V PRB.V PUM.V PXR.V RCR.V RCZ.V RDK.V RDV.TO RKY.V ROS.V ROX.V RRO.V RXL.AX SBB.V SBR.AX SDN.V SEM.V SGC.V SLK.V SLR.TO SLT SMM.AX SMZ.V SNU.V SOX.V SPM.TO SRI.AX SRZ.AX SRZ.TO SSC.AX SSE.V SVT.V SWN.V SXL.V SYH.V SYI.V TAM.V TBM.V TCC.V TCK THG.V THMG.OB TM.V TNG.AX TOE.V TREVF.PK TRF.AX TRO.AX TRO.V TRS.V TYE.V TZN.AX UCL.AX URL.AX VED.L VEM.TO WAR.V WEL.V WGR.AX WMT.AX WOO.V WPR.V WTM.TO XAG.V ZAZ.TO ZINC.L ZN.V ZNC.AX ZNC.TO ZOX.L ZZL.L
LC