Do you mean firms you can use to buy Sri Lankan Treasury Bills and Treasury Bonds (i.e., authorised Primary Dealers / bank PD units and major brokers)? If so — here are the top, commonly used institutions (the Central Bank of Sri Lanka appoints and publishes the authorised Primary Dealers). I list major bank PD units and the leading non‑bank Primary Dealers, with a short note for each and authoritative citations.

Major licensed commercial bank Primary Dealer units

• Bank of Ceylon — large state bank with a Primary Dealer unit used widely by retail and institutional clients. (cbsl.gov.lk)
• Commercial Bank of Ceylon (Primary Dealer Unit) — active treasury desk and broad customer access. (cbsl.gov.lk)
• (Other bank PD units listed by the Central Bank include units of People’s Bank, Hatton National Bank, National Savings Bank and others — see the CBSL authorised PD list for the full, current roster.) (cbsl.gov.lk)

Leading non‑bank (dedicated) Primary Dealers

• First Capital Treasuries PLC (First Capital) — one of the largest non‑bank PDs and frequently cited market leader. (firstcapital.lk)
• HNB Securities Limited (Hatton National Bank’s PD arm) — Primary Dealer offering direct access to T‑Bills and T‑Bonds. (hnbsecurities.lk)
• NSB Fund Management Co. Ltd (NSB FMC) — a dedicated Primary Dealer and subsidiary of National Savings Bank that services institutional and retail clients. (nsbfmc.lk)
• WealthTrust Securities Ltd (WealthTrust) — active non‑bank Primary Dealer with an online portal for auction participation. (wealthtrust.lk)
• Capital Alliance PLC — investment banking group with a Primary Dealer arm used by many investors. (en.wikipedia.org)

Important operational notes (recent regulatory context)

• The authoritative list and status (appointments, suspensions, additions) of Primary Dealers is maintained by the Central Bank of Sri Lanka — check the CBSL “Authorised Primary Dealers / Primary Dealers” page for the current list and any licensing changes. (cbsl.gov.lk)
• Some firms (e.g., Perpetual Treasuries, Pan Asia Bank PD unit) have had their Primary Dealer activities suspended at times; suspensions or regulatory changes do occur and may affect which firms you can use. Confirm current status on the CBSL website before transacting. (economynext.com)

How to choose one

• For retail investors: bank PD units (Bank of Ceylon, Commercial Bank, People’s Bank, HNB) are convenient because you can use existing branch/online banking relationships. (cbsl.gov.lk)
• For institutional or active secondary‑market trading: non‑bank PDs (First Capital Treasuries, NSB FMC, WealthTrust, Capital Alliance) often provide more specialised trading/repo/custody services. (firstcapital.lk)

If you want, I can:

• Pull the Central Bank’s current authorised Primary Dealer list (with the exact date it was published), or
• Compare fees, services, and how to open an account with 3–5 specific PDs (bank vs non‑bank).