I can't find my Seniors Card can I get a replacement

https://www.service.nsw.gov.au/transaction/apply-nsw-seniors-card

Apply for NSW Seniors Card

Go to work force services, r a care Center for Seniors

How do I get a seniors myki?

New Seniors Card program applicants receive a seniors myki for free as part of their Seniors Card application. If you don't already have your seniors myki, contact Public Transport Victoria (PTV) on www.ptv.vic.gov.au or by calling 1800 800 007 between 6am and midnight daily. Once you have your seniors myki, you can top it up at close to 800 retailers including:

• All 7-Eleven stores.
• The ticket office window at Premium Stations and staffed V/Line commuter stations.
• From a myki machine located at all train stations and major tram and bus interchanges.
• Via the PTV website or phone number above.

Remember - it's a condition that you carry your Seniors Card at all times when travelling on public transport as proof of your concession entitlement.

"When applying for a Victorian Seniors Card you'll also receive a free Seniors myki"

Seniors Card https://www.ptv.vic.gov.au/tickets/fares/concession/seniors

No you have to apply to the state you live in.
NSW permanent residents aged 60 or over, who average no more than 20 hours' paid work a week across a 12-month period, can apply for a NSW Seniors Card. This free card gives you discounts and special offers at thousands of businesses across NSW. If you have a valid green Medicare Card you can apply for a NSW Seniors Card online.
If your card is lost, damaged or destroyed, you can Replace a NSW Seniors Card.

go to center link and advise of the stolen cards
apply for new ones
as to the medicare card, your regular doctor will have it on record and it will remain valid until you get a new one