Now the Cetme and G3/HK91 pattern rifles can swap magazines but the Cetme magazine well can be a few thousandths deeper than the G3 magazines are designed for but with a quick swipe of the file they can normally be used .
This is not a complete list I'm sure
5 Rd steel Cetme $10.00-$25.00
http://gunmagwarehouse.com/used-military-surplus-cetme-c-308-dbl-stack-5-round-magazine.html
http://www.keepshooting.com/cetme-5-round-magazine.html
https://www.libertytreecollectors.com/productcart/pc/viewPrd.asp?idproduct=452
5 Rd steel HK G3 <$32.95
http://www.robertrtg.com/store/pc/RDTS-5RD-STEEL-G3-MAGAZINE-24p2158.htm
http://www.hessenantique.com/German_CETME_G3_HK_91_5_Round_Steel_Magazines_p/s19653599.htm
5 Rd aluminum HK G3 $29.95
https://www.hkparts.net/shop/pc/5-Round-Magazine-HK91-G3-PTR-Aluminum-111p16275.htm
10 Rd steel HK G3 $49.95
https://www.hkparts.net/shop/pc/10-Round-Magazine-Steel-HK-G3-91-PTR-111p1607.htm
10 Rd aluminum HK G3 $39.95
https://www.hkparts.net/shop/pc/10-Round-Magazine-Aluminum-HK-91-HK-G3-PTR-111p351.htm
10 Rd polymer Thermold G3 $13.25- $19.95
http://www.thermoldmagazines.com/hk-91-10-762x51/
https://www.budsgunshop.com/catalog/product_info.php/products_id/57886
15 Rd aluminum G3 $37.95
https://www.hkparts.net/shop/pc/viewPrd.asp?idproduct=17006&idcategory=111
20 Rd steel Cetme $3.96
http://www.jgsales.com/c308-and-cetme-20rd-surplus-308-magazine,-vg,-used.-p-2415.html
20 Rd steel HK G3 $4.95 - $9.95
http://www.robertrtg.com/store/pc/STEEL-HK91-G3-20RD-MAGAZINE-24p2127.htm
https://www.cheaperthandirt.com/product/mag-h-and-k-g3-762x51mm-steel-20-round-military-surplus-made-in-germany-used-condition-grade-ii-mag-303.do?sortby=priceAscend&refType=&from=fn
20 Rd aluminum HK G3 $4.97 -$9.95
http://www.robertrtg.com/store/pc/HK91-G3-20RD-ALUMINUM-MAGAZINE-LIKE-NEW-24p2898.htm
https://www.cheaperthandirt.com/product/mag-h-and-k-g3-762x51mm-aluminum-20-round-original-military-mag-304.do?sortby=priceAscend&refType=&from=fn
20 Rd polymer Thermold G3 $13.99_$19.95
http://www.thermoldmagazines.com/hk-91-20-762x51/
http://www.impactguns.com/thermold-hk9-magazines-308-20-round-black-hk9120762x51-895389002192.aspx
http://shopwilsoncombat.com/HK-91-Magazine-762x51mm-20-Round-Polymer-Thermold/productinfo/HK-MAG/
30 Rd steel cetme $??.??
30 Rd African magazine Looks like a HK $???.??
30 Rd steel HK G3 $89.95
https://www.hkparts.net/shop/pc/viewPrd.asp?idproduct=16747&idcategory=111
30 Rd steel National Magazine Inc. G3 $9.97
https://www.cheaperthandirt.com/product/national-magazine-h-and-k-91-rifle-magazine-308-winchester-30-rounds-874375001555.do?sortby=priceAscend&refType=&from=fn
40 Rd steel HK RTDS G3 $79.99
http://www.robertrtg.com/store/pc/RDTS-40RD-G3-MAGAZINE-24p2157.htm
https://www.hkparts.net/shop/pc/viewPrd.asp?idproduct=218&idcategory=111
50 Rd polymer drum X products $249.99
https://www.hkparts.net/shop/pc/50-Round-Drum-For-HK-91-G3-PTR-Rifles-42p1283.htm
https://www.xproducts.com/product/x-91-50-round-drum-magazine-hk91-g3/
https://www.cheaperthandirt.com/product/x-products-hk-91-ptr-91-drum-magazine-308-win-50-rounds-713757989916.do?from=fn&sortby=shortDescend
100 Rd polymer Beta company drum $450.00
http://www.betaco.com/cmag_product_details.asp?product=20
https://www.hkparts.net/shop/pc/100-Round-Drum-for-HK91-G3-PTR-91-9p2293.htm