No idea about selling shitcoins but isn’t there any p2p markets to sell tokens for btc? If the portfolio is fiat only, I think Relai offer 1% fees on big orders. Other than that, I don’t have any good recommendations :/

another option is OTC desks:  cumberland or genesis. minimum orders are usually $250k.  https://kyc.cumberland.io/onboard-individual https://genesistrading.com/