They would have to be specifically registered with the Ca DOJ to ship to California .
Why do you want to transfer through a MD FFL as opposed to shipping directly to the CA FFL?
California law requires inbound shipments only from FFLs who are Also registered with California ...
Cal. FFL01 dealers can only accept a firearm from a FFL01 that has paid their fee to be on their (Cal) list. I sold a WWII K98 to a guy in Cal. and even though it was a C&R gun it had to be sent by a local ffl01 that had paid to be on their (Cal) list and had to go to a FFL01 in Cal.
"Cal. FFL01 dealers can only accept a firearm from a FFL01 that has paid their fee to be on their (Cal) list."
This part is true in its specifics: FFL dealer/manufacturer to CA FFL does require registration. but...
Unless something changed recently, a C&R long gun can be sent direct to a CA FFL-03 that also has a valid "Certificate of Eligibility" (COE). The receiving -03 has to do some additional paperwork w/CA's DOJ on their end but that's not the seller's concern.
Firearms in general can also be sent by individuals (or FFL-03's for C&R) to a CA FFL dealer/manufacturer w/o the registration crap.
Finding a receiving CA FFL that is willing to do it, now that's a different story !!
But they do exist
see #2, #4 here (site is dated 2020 at the bottom)
https://oag.ca.gov/firearms/cflcfaqs
2) I am not an FFL but I want to ship a firearm to a California FFL. Do I have to obtain a Firearms Shipment Approval number before shipping a firearm to California?
No. Only shipments from Federal Firearms Licensees (FFL) require a Firearms Shipment Approval number.
<well, FFL's other then -03 and -06 that is>
4) Are any California FFLs exempt from the CFLC verification approval requirement?
Yes. The CFLC program does not apply to shipments made by Type 03 (curio and relic collectors) and Type 06 (ammunition dealers) FFLs.
also see
https://oag.ca.gov/firearms/cflcoverview